Rename CheckUnsnaps -> CheckUnsnappedObjects

Will potentially have `CheckUnsnappedKiai` or similar later, so this is worth specifying.

Also consistent with `CheckConcurrentObjects`, which will likely have a `CheckConcurrentLines` later.

osu.Game/Rulesets/Edit/BeatmapVerifier.cs

@@ -25,7 +25,7 @@ namespace osu.Game.Rulesets.Edit
             new CheckAudioQuality(),
 
             // Compose
-            new CheckUnsnaps(),
+            new CheckUnsnappedObjects(),
             new CheckConcurrentObjects()
         };