[Release Notes] Mention Clang-tidy misc-unused-using-decls check.
[Release Notes] Mention Clang-tidy misc-unused-using-decls check.


git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@266770 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra