Don't short-circuit TypeRefinementContext building for functions

`buildTypeRefinementContextHierarchyDelayed()` is already guarded
behind a request, so it doesn't need its own logic for eliminating
redundant computation. Remove that logic, which incorrectly assumed
that the TRC was built for a function if the function body has already
been parsed.

Author: DougGregor

lib/Sema/TypeCheckAvailability.cpp

@@ -1199,7 +1199,7 @@ void TypeChecker::buildTypeRefinementContextHierarchyDelayed(SourceFile &SF, Abs
   if(!RootTRC)
     return;
 
-  if (AFD->getBodyKind() != AbstractFunctionDecl::BodyKind::Unparsed)
+  if (AFD->getLoc().isInvalid())
     return;
 
   // Parse the function body.