qt-mobility: remove /usr/lib from ld rpath-link option
Remove /usr/lib from ld rpath-link option to fix the below build error:
bitbake_build/tmp/sysroots/x86-kvm-guest/usr/lib/libpng16.so.16:
undefined reference to `inflateReset2@ZLIB_1.2.3.4'
since sysroot seems not work for rpath-link, and "rpath-link,/usr/lib" makes
ld to search host libraries for target libraries, once host has different
version zlib, the error will happen.
qmake uses QT_MOBILITY_LIB to generate "rpath-link,/usr/lib" when do_configure
but we can not add sysroot into QT_MOBILITY_LIB, since QT_MOBILITY_LIB is dir
which libraries will be installed to, so I remove this dir from rpath-link
before do_compile
