[AST][NFC] Remove a superfluous enum in ObjCMethodDeclBitfields added in r338641
[AST][NFC] Remove a superfluous enum in ObjCMethodDeclBitfields added in r338641

I originally added this enum to avoid including Basic/IdentifierTable.h
in AST/DeclBase.h. However I did not realise it is already included
transitively by AST/DeclarationName.h. Therefore remove this enum and
explicitly include Basic/IdentifierTable.h



git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@342731 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang