Remove unused forward declarations

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@175328 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Sema/Ownership.h

@@ -23,13 +23,10 @@
 //===----------------------------------------------------------------------===//
 
 namespace clang {
-  class Attr;
   class CXXCtorInitializer;
   class CXXBaseSpecifier;
   class Decl;
-  class DeclGroupRef;
   class Expr;
-  class NestedNameSpecifier;
   class ParsedTemplateArgument;
   class QualType;
   class Stmt;