More #include cleaning

More #include cleaning
 - Kill unnecessary #includes in .cpp files. This is an automatic
   sweep so some things removed are actually used, but happen to be
   included by a previous header. I tried to get rid of the obvious
   examples and this was the easiest way to trim the #includes in one
   fell swoop.
 - We now return to regularly scheduled development.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@54632 91177308-0d34-0410-b5e6-96231b3b80d8