Remove unneded link-time dependency on libz and libexpat

[jankatins]

My debian build complained about them that they are linked in but that this is not needed. No idea why. My grive works fine with these changes.

[Tatsh]

You should delete the lines instead of commenting them out.

[Tatsh]

Also you can remove these lines in libgrive/CMakeLists.txt:

if ( ZLIB_FOUND )
        set( OPT_LIBS   ${OPT_LIBS}     ${ZLIB_LIBRARIES} )
endif ( ZLIB_FOUND )

[jankatins]

done

[vitalif]

Thanks, merged