[clang] [Clang] Drop workaround for old gcc versions (PR #78803)

[via cfe-commits]

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@@ -6081,11 +6081,10 @@ QualType
 TreeTransform<Derived>::TransformFunctionProtoType(TypeLocBuilder &TLB,
                                                    FunctionProtoTypeLoc TL) {
   SmallVector<QualType, 4> ExceptionStorage;
-  TreeTransform *This = this; // Work around gcc.gnu.org/PR56135.
   return getDerived().TransformFunctionProtoType(
       TLB, TL, nullptr, Qualifiers(),
       [&](FunctionProtoType::ExceptionSpecInfo &ESI, bool &Changed) {
-        return This->getDerived().TransformExceptionSpec(
+        return this->getDerived().TransformExceptionSpec(
----------------
cor3ntin wrote:

```suggestion
        return getDerived().TransformExceptionSpec(
```

https://github.com/llvm/llvm-project/pull/78803