Delete EvalState::addToSearchPath

This function is now trivial enough that it doesn't need to exist.

`EvalState` can still be initialized with a custom search path, but we
don't have a need to mutate the search path after it has been
constructed, and I don't see why we would need to in the future.

Fixes NixOS#8229

src/libexpr/eval.cc

@@ -527,9 +527,9 @@ EvalState::EvalState(
     /* Initialise the Nix expression search path. */
     if (!evalSettings.pureEval) {
         for (auto & i : _searchPath.elements)
-            addToSearchPath(SearchPath::Elem {i});
+            searchPath.elements.emplace_back(SearchPath::Elem {i});
         for (auto & i : evalSettings.nixPath.get())
-            addToSearchPath(SearchPath::Elem::parse(i));
+            searchPath.elements.emplace_back(SearchPath::Elem::parse(i));
     }
 
     if (evalSettings.restrictEval || evalSettings.pureEval) {

src/libexpr/eval.hh

@@ -341,8 +341,6 @@ public:
         std::shared_ptr<Store> buildStore = nullptr);
     ~EvalState();
 
-    void addToSearchPath(SearchPath::Elem && elem);
-
     SearchPath getSearchPath() { return searchPath; }
 
     /**

src/libexpr/parser.y

@@ -736,12 +736,6 @@ Expr * EvalState::parseStdin()
 }
 
 
-void EvalState::addToSearchPath(SearchPath::Elem && elem)
-{
-    searchPath.elements.emplace_back(std::move(elem));
-}
-
-
 SourcePath EvalState::findFile(const std::string_view path)
 {
     return findFile(searchPath, path);