Remove unused AST matcher.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@216901 91177308-0d34-0410-b5e6-96231b3b80d8
[clang-tidy] Add check for possibly incomplete switch statements

While clang warns about a possibly incomplete switch statement when
switching over an enum variable and failing to cover all enum values
(either explicitly or with a default case), no such warning is emitted
if a plain integer variable is used as switch variable.

Add a clang-tidy check to diagnose these scenarios.

No fixit hint is provided since there are multiple possible solutions.
Catch switches on *all* non-enum types
Formatting: end-of-namespace identifiers
Remove unneeded and unwanted include