'Q' object is needed only for complex queries

[johnmhoran]

From @tdruez 's comments in #875 .

Q object is not needed here, it is only required for complex query such as applying OR between filters such as https://github.com/nexB/vulnerablecode/pull/813/files#diff-3e8fc96d993d0bd8585642f68239732a30a19b7ec100a36ee5d21e209625ff81R202.
This comment applies to all the place you have a single Q in your filter().