Remove a couple typedefs for things in the clang namespace with the same name. Remove a typedef that matches an identical one in the clang namespace.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220954 91177308-0d34-0410-b5e6-96231b3b80d8
Remove CastKind typedef from CastExpr since CastKind is in the clang namespace.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220955 91177308-0d34-0410-b5e6-96231b3b80d8
Remove StorageClass typedefs from VarDecl and FunctionDecl since StorageClass is in the clang namespace.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220956 91177308-0d34-0410-b5e6-96231b3b80d8