Fixed the query for imported actors and some other potential edge cases.
Unsetting the 'target' field in SpecialDeletedContributions alone should
be sufficient, but I would rather like to keep the behaviour the same
with ContribsPager, which is used by more users and using
`$this->targetUser->getName()` is known to be ok so far.
Also, renamed some variables to match the parent class method signature
to avoid confusion.
Bug: T372444
Bug: T404230
Change-Id: I318ec7f30174087f988536f5196ff81e99241c9b
(cherry picked from commit dda0d4dfcd712b976e542cd688a3ab1c45051e7d)
6677a9ce4b