No need to force-create clang-tools-extra lit.site.cfg

The make (all) target takes care of creating lit configs and auto-generating
tests. The problem with the original 'lit.site.cfg' target is it's not
recursive and doesn't fully create everything necessary for testing
clang-tools-extra.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176374 91177308-0d34-0410-b5e6-96231b3b80d8