[CMake] Temporarily remove the LLVM_ENABLE_IDE option

All uses of this option have been removed, and the intent is to change the purpose and default value of this option. To prevent it from having impacts on users, this patch temporarily removes the option and purges it from CMake caches. In a few days, once this has propagated to contributors I will re-introduce the option with the new default value.

llvm-svn: 344219