Make git-annex copy --from --to --fast actually fast

Eg when the destination is logged as containing a file, skip
actively checking that it does contain it.

Note that --fast does not prevent other verifications of content
location that are done in a copy --from --to. Perhaps it could, but this
change will already avoid the real unnecessary work of operating on
files that are already in the remote.

And avoiding other verifications
might cause it to fail if the location log thinks that --to does not
contain the content but does. Such complications with `git-annex copy
--to remote --fast` led to commit d006586cd0
which added a note that gets displayed when that fails, mentioning it
might be due to --fast being enabled.

copy --from --to is already complicated enough without needing to worry
about such edge cases, so continuing to doing some verification of
content location after the initial --fast filtering seems ok.

Sponsored-by: Dartmouth College's DANDI project

Command/Move.hs

@@ -345,7 +345,13 @@ fromToStart removewhen afile key ai si src dest =
 					starting (describeMoveAction removewhen) (OnlyActionOn key ai) si $
 						fromToPerform src dest removewhen key afile
   where
-	somethingtodo = pure (Remote.uuid src /= Remote.uuid dest)
+	somethingtodo
+		| Remote.uuid src == Remote.uuid dest = return False
+		| otherwise = do
+			fast <- Annex.getRead Annex.fast
+			if fast && removewhen == RemoveNever
+				then not <$> expectedPresent dest key
+				else return True
 
 {- When there is a local copy, transfer it to the dest, and drop from the src.
  -