Remove clang/ModuleInfo.txt

The script build-for-llvm-top.sh and LLVM's ModuleInfo.txt are gone
since a long time (commit d20ea7dc in November 2011), and llvm-top
itself has even been removed from llvm-archive (it can be found here:
https://github.com/llvm/llvm-archive/tree/cab7f8f160f0bd8d20d9a4036aa4083f2bc2740a/llvm-top
) so delete Clang's ModuleInfo.txt as well.

Differential Revision: https://reviews.llvm.org/D152995