Trim some includes. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220877 91177308-0d34-0410-b5e6-96231b3b80d8
clang-format: Cut more clangAST dependencies.

Hopefully fixing windows builds.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220878 91177308-0d34-0410-b5e6-96231b3b80d8
Sink a #include while we're here. NFC.

Format.h doesn't use stack.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220879 91177308-0d34-0410-b5e6-96231b3b80d8