fix: dublicate dtmf

dialer/android/app/src/main/kotlin/com/icing/dialer/activities/MainActivity.kt

@@ -217,15 +217,6 @@ class MainActivity : FlutterActivity() {
                         checkAndRequestDefaultDialer()
                         result.success(true)
                     }
-                    "sendDtmfTone" -> {
-                        val digit = call.argument<String>("digit")
-                        if (digit != null) {
-                            val success = MyInCallService.sendDtmfTone(digit)
-                            result.success(success)
-                        } else {
-                            result.error("INVALID_ARGUMENT", "Digit is null", null)
-                        }
-                    }
                     else -> result.notImplemented()
                 }
             }