sip-native: inherit qmake2 instead of qt4x11

* it seems enough
* inherit qt4x11 adds dependency on target qt4-x11-free, which is bad,
  because we don't need it and it's causing different sstate checksum:
  $ bitbake-diffsigs
    stamps.1347348593/nokia900/x86_64-linux/sip-native-4.13.3-r0.do_configure.sigdata.6e44871660ef91eab5ee4d56e55b6728
    stamps.1347348593/om-gta02/x86_64-linux/sip-native-4.13.3-r0.do_configure.sigdata.cdaf666b98c2c6ccfb710743dcdbd988
      Hash for dependent task qt4-x11-free_4.8.1.bb.do_populate_sysroot changed from 79234aca07686c1d97782e21fc098071 to 7e9ba3de3ba9f709a5d9ef5abadb2d9e

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>