🧹 Sentinel: Remove unused onDeleteMultiCharInput method

Removed the empty and unused `onDeleteMultiCharInput` method from `StatsUtils.kt` to keep the codebase clean and reduce maintenance overhead. This method had no active callers.

Author: LeanBitLab

.jules/bolt.md

@@ -34,9 +34,6 @@ object StatsUtils {
     fun onBackspaceSelectedText(selectedTextLength: Int) {
     }
 
-    fun onDeleteMultiCharInput(multiCharLength: Int) {
-    }
-
     fun onRevertAutoCorrect() {
     }