Remove unneeded liblxqt dependencies

Actually liblxqt-mount is totally independent from liblxqt. liblxqt is used
only to get LXQT_VERSION LXQT_MAJOR_VERSION.
We need a better way to do this and drop totally liblxqt dependency.

Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>