Revert rr159875, "Implement -Wpedantic and --no-pedantic to complement...

Revert rr159875, "Implement -Wpedantic and --no-pedantic to complement -Weverything." It broke several builds.

I suspect FileCheck might match assertion failure, even if clang/test/Misc/warning-flags.c passed the test.

> 0. Program arguments: bin/./clang -### -pedantic -Wpedantic clang/test/Driver/warning-options.cpp

llvm-svn: 159886