Update clang attribute document.

Remove the instructions on manually adding boilerplate code of AttributeList::Kind and AttributeList::getKind().
Both are now generated by tblgen.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@158386 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed