Remove LLVM_CONFIG from config headers

It appears to be dead, and it needlessly caused me to rebuild all of
LLVM when I changed CMAKE_INSTALL_PREFIX.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@293574 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed