sip4 does not conflict with sip anymore

[daizhirui]

sip is now provided as a python package that is installed at /usr/lib/python*/site-packages/sipbuild, which does not conflict with sip4 at all. Same for python-sip4, it does not conflict with sip and it should not be labeled as providing python-sip because python-sip should be preserved for the latest sip release.