[AST] Remove ASTContext from getThisType (NFC)

Summary:
https://reviews.llvm.org/D54862 removed the usages of `ASTContext&` from
within the `CXXMethodDecl::getThisType` method. Remove the parameter
altogether, as well as all usages of it. This does not result in any
functional change because the parameter was unused since
https://reviews.llvm.org/D54862.

Test Plan: check-clang

Reviewers: akyrtzi, mikael

Reviewed By: mikael

Subscribers: mehdi_amini, dexonsmith, cfe-commits

Differential Revision: https://reviews.llvm.org/D56509

llvm-svn: 350914
diff --git a/clang/lib/CodeGen/CGDebugInfo.cpp b/clang/lib/CodeGen/CGDebugInfo.cpp
index 7ebbfbe..41f8721 100644
--- a/clang/lib/CodeGen/CGDebugInfo.cpp
+++ b/clang/lib/CodeGen/CGDebugInfo.cpp
@@ -1428,8 +1428,7 @@
   if (Method->isStatic())
     return cast_or_null<llvm::DISubroutineType>(
         getOrCreateType(QualType(Func, 0), Unit));
-  return getOrCreateInstanceMethodType(Method->getThisType(CGM.getContext()),
-                                       Func, Unit);
+  return getOrCreateInstanceMethodType(Method->getThisType(), Func, Unit);
 }
 
 llvm::DISubroutineType *CGDebugInfo::getOrCreateInstanceMethodType(
@@ -4064,7 +4063,7 @@
       QualType type;
       if (auto *Method =
               cast_or_null<CXXMethodDecl>(blockDecl->getNonClosureContext()))
-        type = Method->getThisType(C);
+        type = Method->getThisType();
       else if (auto *RDecl = dyn_cast<CXXRecordDecl>(blockDecl->getParent()))
         type = QualType(RDecl->getTypeForDecl(), 0);
       else