Revert "cmake: only set output paths with multiple outputs"

This reverts commit be1b2253.

The commit broke Qt modules using CMake because they disable setOutputFlags.

There is no need to have these flags limited to multiple output derivations since it
should just work. If it does not, it is a bug that should be fixed as per
https://github.com/jtojnar/cmake-snips#assuming-cmake_install_dir-is-relative-path
Likewise, having a variable to disable passing the flags is also unnecessary,
since CMake, unlike some configure scripts, ignores unknown flags. And if a person
does not like the values, they can just override them by passing the offending
flag with a different value to cmakeFlags.