Remove swift::createTypeChecker

Replace it with the "legacy semantic queries" bit. The remaining client
of this bit is SourceKit, which appears to require this bit be set
conditionally so certain semantic property wrapper requests return
a sentinel value.

We should migrate these requests to a syntactic interface as soon as
possible.

rdar://60516325

tools/SourceKit/lib/SwiftLang/SwiftIndexing.cpp

@@ -200,7 +200,7 @@ static void indexModule(llvm::MemoryBuffer *Input,
   }
 
   // Setup a typechecker for protocol conformance resolving.
-  (void)createTypeChecker(Ctx);
+  Ctx.setLegacySemanticQueriesEnabled();
 
   SKIndexDataConsumer IdxDataConsumer(IdxConsumer);
   index::indexModule(Mod, IdxDataConsumer);
@@ -314,7 +314,7 @@ void SwiftLangSupport::indexSource(StringRef InputFile,
   }
 
   // Setup a typechecker for protocol conformance resolving.
-  (void)createTypeChecker(CI.getASTContext());
+  CI.getASTContext().setLegacySemanticQueriesEnabled();
 
   SKIndexDataConsumer IdxDataConsumer(IdxConsumer);
   index::indexSourceFile(CI.getPrimarySourceFile(), IdxDataConsumer);