Fix _get_cache_schemas by removing relation identifiers

[jtcohen6]

resolves #52

Problem

We were running one caching query per relation (resource) defined in the project

Solution

We should only run one caching query per schema, by dropping the relation-specific identifier within _get_cache_schemas

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX