Update error message text.

Update error message text.

Previously if an enumeration was used in a nested name specifier in pre-C++11
language dialect, error message was 'XXX is not a class, namespace, or scoped
enumeration'. This patch removes the word 'scoped' as in C++11 any enumeration
may be used in this context.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@226410 91177308-0d34-0410-b5e6-96231b3b80d8