Don't pass acceptdocs down to parents filter

This may result in something other than FixedBitSet and cause an error.

Its wasteful at least, we already pass it to the scorer. But its possible if acceptDocs are non-null that we could get back a BitsFilteredDocIdSet or similar, which would cause an exception (e.g. during delete by query).

I don't have a test yet. Only applies to 1.x and not master, as we fixed the type safety in master/lucene 5