Revert "Add CC_Win64ThisCall and set it in the necessary places."

This reverts commit 126863.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@126886 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGObjC.cpp b/lib/CodeGen/CGObjC.cpp
index 6ae1ac8..5d34907 100644
--- a/lib/CodeGen/CGObjC.cpp
+++ b/lib/CodeGen/CGObjC.cpp
@@ -140,8 +140,7 @@
 
   CurGD = OMD;
 
-  StartFunction(OMD, OMD->getResultType(), Fn, Args, OMD->getLocStart(),
-                CC_Default);
+  StartFunction(OMD, OMD->getResultType(), Fn, Args, OMD->getLocStart());
 }
 
 void CodeGenFunction::GenerateObjCGetterBody(ObjCIvarDecl *Ivar,