Revert "Sema: Infer '@_usableFromInline' imports by looking at references from inlinable functions (#16326)"

This reverts commit ee6e190. It's not
sufficient to solve the problem, and the choices were to do something
more complicated, or just take a simple brute force approach. We're
going with the latter.

Author: jrose-apple

include/swift/AST/Module.h

@@ -791,7 +791,7 @@ class SourceFile final : public FileUnit {
   /// This is the list of modules that are imported by this module.
   ///
   /// This is filled in by the Name Binding phase.
-  MutableArrayRef<std::pair<ModuleDecl::ImportedModule, ImportOptions>> Imports;
+  ArrayRef<std::pair<ModuleDecl::ImportedModule, ImportOptions>> Imports;
 
   /// A unique identifier representing this file; used to mark private decls
   /// within the file to keep them from conflicting with other files in the
@@ -897,8 +897,6 @@ class SourceFile final : public FileUnit {
 
   bool hasTestableImport(const ModuleDecl *module) const;
 
-  void markUsableFromInlineImport(const ModuleDecl *module);
-
   void clearLookupCache();
 
   void cacheVisibleDecls(SmallVectorImpl<ValueDecl *> &&globals) const;

lib/AST/Module.cpp

@@ -1287,14 +1287,6 @@ bool SourceFile::hasTestableImport(const swift::ModuleDecl *module) const {
   });
 }
 
-void SourceFile::markUsableFromInlineImport(const ModuleDecl *module) {
-  for (auto &Import : Imports) {
-    if (Import.first.second == module) {
-      Import.second |= ImportFlags::UsableFromInline;
-    }
-  }
-}
-
 void SourceFile::clearLookupCache() {
   if (!Cache)
     return;

lib/Sema/TypeCheckAvailability.cpp

@@ -2509,19 +2509,12 @@ bool AvailabilityWalker::diagAvailability(const ValueDecl *D, SourceRange R,
       return true;
   }
 
-  if (FragileKind) {
-    if (R.isValid()) {
+  if (FragileKind)
+    if (R.isValid())
       if (TC.diagnoseInlinableDeclRef(R.Start, D, DC, *FragileKind,
                                       TreatUsableFromInlineAsPublic))
         return true;
 
-      auto *SF = cast<SourceFile>(DC->getModuleScopeContext());
-      auto *M = D->getDeclContext()->getParentModule();
-      if (SF->getParentModule() != M)
-        SF->markUsableFromInlineImport(M);
-    }
-  }
-
   if (TC.diagnoseExplicitUnavailability(D, R, DC, call))
     return true;