Ignore test Inputs globally and remove redundant lit.local.cfg files

By adding a default config.excludes pattern we can avoid individual
suppressions in subdirectories.

This matches LLVM's lit.cfg which also excludes a few other common non-test
filenames for consistency.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194814 91177308-0d34-0410-b5e6-96231b3b80d8