Remove model association presets

Fixes compile error resulting from including the same mixin twice:

```
There was a problem expanding macro 'setup_initialize'

Code in macro 'setup'

 1 | Avram::Model.setup_initialize(
     ^
Called macro defined in lib/avram/src/avram/model.cr:176:3

 176 | macro setup_initialize(columns, *args, **named_args)

Which expanded to:

 >  9 |           @price,
 > 10 |
 > 11 |           @credit_note_id,
                  ^
Error: duplicated def parameter name: credit_note_id
```

spec/support/app/src/models/credit_note_item.cr

@@ -1,5 +1,6 @@
 class CreditNoteItem < BaseModel
   include Bill::CreditNoteItem
+  include Bill::BelongsToCreditNote
 
   table :credit_note_items {}
 end

spec/support/app/src/models/invoice_item.cr

@@ -1,5 +1,6 @@
 class InvoiceItem < BaseModel
   include Bill::InvoiceItem
+  include Bill::BelongsToInvoice
 
   table :invoice_items {}
 end

src/bill/models/credit_note.cr

@@ -3,13 +3,8 @@ module Bill::CreditNote
     include Bill::ParentAmount
     include Bill::ReferenceColumns
 
-    {% if Avram::Model.all_subclasses.find(&.name.== :Invoice.id) %}
-      include Bill::BelongsToInvoice
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :CreditNoteItem.id) %}
-      include Bill::HasManyCreditNoteItems
-    {% end %}
+    # include Bill::BelongsToInvoice
+    # include Bill::HasManyCreditNoteItems
 
     column description : String?
     column notes : String?

src/bill/models/credit_note_item.cr

@@ -1,8 +1,6 @@
 module Bill::CreditNoteItem
   macro included
-    {% if Avram::Model.all_subclasses.find(&.name.== :CreditNote.id) %}
-      include Bill::BelongsToCreditNote
-    {% end %}
+    # include Bill::BelongsToCreditNote
 
     column description : String
     column quantity : Quantity

src/bill/models/invoice.cr

@@ -3,17 +3,9 @@ module Bill::Invoice
     include Bill::ReferenceColumns
     include Bill::ParentNetAmount
 
-    {% if Avram::Model.all_subclasses.find(&.name.== :CreditNote.id) %}
-      include Bill::HasManyCreditNotes
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :InvoiceItem.id) %}
-      include Bill::HasManyInvoiceItems
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :User.id) %}
-      include Bill::BelongsToUser
-    {% end %}
+    # include Bill::BelongsToUser
+    # include Bill::HasManyCreditNotes
+    # include Bill::HasManyInvoiceItems
 
     column business_details : String
     column description : String?

src/bill/models/invoice_item.cr

@@ -1,8 +1,6 @@
 module Bill::InvoiceItem
   macro included
-    {% if Avram::Model.all_subclasses.find(&.name.== :Invoice.id) %}
-      include Bill::BelongsToInvoice
-    {% end %}
+    # include Bill::BelongsToInvoice
 
     column description : String
     column quantity : Quantity

src/bill/models/receipt.cr

@@ -2,9 +2,7 @@ module Bill::Receipt
   macro included
     include Bill::ReferenceColumns
 
-    {% if Avram::Model.all_subclasses.find(&.name.== :User.id) %}
-      include Bill::BelongsToUser
-    {% end %}
+    #include Bill::BelongsToUser
 
     column amount : Amount
     column business_details : String

src/bill/models/transaction.cr

@@ -2,21 +2,10 @@ module Bill::Transaction
   macro included
     include Bill::ReferenceColumns
 
-    {% if Avram::Model.all_subclasses.find(&.name.== :CreditNote.id) %}
-      include Bill::CreditNoteTransactionSource
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :Invoice.id) %}
-      include Bill::InvoiceTransactionSource
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :Receipt.id) %}
-      include Bill::ReceiptTransactionSource
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :User.id) %}
-      include Bill::BelongsToUser
-    {% end %}
+    # include Bill::BelongsToUser
+    # include Bill::CreditNoteTransactionSource
+    # include Bill::InvoiceTransactionSource
+    # include Bill::ReceiptTransactionSource
 
     column amount : Amount
     column description : String

src/bill/models/user.cr

@@ -2,21 +2,11 @@ module Bill::User
   abstract def billing_details : String
 
   macro included
-    {% if Avram::Model.all_subclasses.find(&.name.== :CreditNote.id) %}
-      include Bill::HasManyCreditNotesThroughInvoices
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :Invoice.id) %}
-      include Bill::HasManyInvoices
-    {% end %}
-
-    {% if Avram::Model.all_subclasses.find(&.name.== :Receipt.id) %}
-      include Bill::HasManyReceipts
-    {% end %}
+    # include Bill::HasManyCreditNotesThroughInvoices
+    # include Bill::HasManyInvoices
+    # include Bill::HasManyReceipts
 
     {% if Avram::Model.all_subclasses.find(&.name.== :Transaction.id) %}
-      include Bill::HasManyTransactions
-
       {% if Avram::Model.all_subclasses.find(&.name.== :CreditNote.id) %}
         include Bill::CreditNotesAmount
       {% end %}