pkgdata.py: avoid target-sdk-dummy-provides to mess things up

pkgdata.py: avoid target-sdk-dummy-provides to mess things up

Sometimes we meet the following failure for the test_lookup_recipe
test case.

  AssertionError: 'zlib\nbusybox is in the RPROVIDES of target-sdk-provid[32 chars]ummy' != 'zlib\nbusybox'
    zlib
  + busybox- busybox is in the RPROVIDES of target-sdk-provides-dummy:
  - target-sdk-provides-dummy

This is because target-sdk-provides-dummy rprovides busybox.

So clean things up to avoid failure.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Armin Kuster <akuster808@gmail.com>