Move lowering of required KF5 versions to mk-file
* Makefile.am: Delete referenced patches * patches/kleopatra/lower-kf5-required.patch: obsolete * patches/libkleo/lower-kf5-required.patch: obsolete * src/gpg4win.mk.in: Replaced the required versions for KF5, KMIME, LIBKLEO and GPGME with fixed values, so manual patching will be obsolete