Revert "[CMake] Fix ncurses/zlib in LLVM_SYSTEM_LIBS for Windows GNU"

It broke Chromium's llvm build:

 CMake Error at lib/Support/CMakeLists.txt:13 (string):
   string sub-command REGEX, mode REPLACE: regex "^()" matched an empty
   string.
 Call Stack (most recent call first):
   lib/Support/CMakeLists.txt:223 (get_system_libname)

This reverts commit 2b3807d8 /  https://reviews.llvm.org/D86434