find-delta: minor preparatory change We are about to add more item in the cachedelta object, so lets access the item by index instead of doing a full extensions.

find-delta: rename _isgooddeltainfo Lets move to a more readable name now that we are allowed to. This cannot hurt.

test-revlog-raw: drop the overwrite of dead code The revlog class no longer have a _isgooddeltainfo method for a long time. So overwriting it does not get us anything. The test have been wrapping the right code since then anyway.