Drop PolkitQt1::version*() API declaration, never implemented
Seems the version header once was inspired by kdelibs' kdecore/util/kdeversion.h.cmake but missed out the cpp counterpart.
Given no-one has ever complained about the missing runtime-version check option, just dropping it then.
Tested with building KF's kauth against it, which uses the version header and POLKITQT1_IS_VERSION.