AST: Don't force RequirementMachine creation in getOrCreateGenericSignatureBuilder()

This was for test coverage before I had any queries ported over, just to
make sure that the completion procedure worked.

Now that all the GenericSignature queries have been ported over, we don't
need this since  we're going to create all the RequirementMachines anyway.

Author: slavapestov

lib/AST/ASTContext.cpp

@@ -1797,10 +1797,6 @@ void ASTContext::registerGenericSignatureBuilder(
 
 GenericSignatureBuilder *ASTContext::getOrCreateGenericSignatureBuilder(
                                                       CanGenericSignature sig) {
-  if (LangOpts.EnableRequirementMachine) {
-    (void) getOrCreateRequirementMachine(sig);
-  }
-
   // Check whether we already have a generic signature builder for this
   // signature and module.
   auto arena = getArena(sig);