refactor: use '--' for int decremention instead of '-= 1'

app/src/main/java/com/github/libretube/ui/adapters/VideosAdapter.kt

@@ -69,7 +69,7 @@ class VideosAdapter(
             it.url?.toID() == videoId
         }.takeIf { it > 0 } ?: return
         streamItems.removeAt(index)
-        visibleCount -= 1
+        visibleCount--
         notifyItemRemoved(index)
         notifyItemRangeChanged(index, itemCount)
     }

app/src/main/java/com/github/libretube/ui/adapters/WatchHistoryAdapter.kt

@@ -34,7 +34,7 @@ class WatchHistoryAdapter(
             DatabaseHolder.Database.watchHistoryDao().delete(history)
         }
         watchHistory.removeAt(position)
-        visibleCount -= 1
+        visibleCount--
         notifyItemRemoved(position)
         notifyItemRangeChanged(position, itemCount)
     }

app/src/main/java/com/github/libretube/ui/views/AutoplayCountdownView.kt

@@ -66,7 +66,7 @@ class AutoplayCountdownView(
             R.string.playing_next,
             currentTimerState.toString()
         )
-        currentTimerState -= 1
+        currentTimerState--
         handler.postDelayed(1000, TIMER_RUNNABLE_TOKEN, this::updateCountdown)
     }