Remove -Wnon-modular-include

But keep -Wnon-modular-include-in-[framework-]module

This warning is too noisy and doesn't really indicate a problem for most
people.  Even though it would only really affect people using
-Weverything, that seems bad so remove it.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@208345 91177308-0d34-0410-b5e6-96231b3b80d8