Revert Add flutter_dtmf, something broke the code compilation.

Author: cloudwebrtc

example/lib/src/callscreen.dart

@@ -1,8 +1,6 @@
 import 'dart:async';
-import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_webrtc/flutter_webrtc.dart';
-import 'package:flutter_dtmf/flutter_dtmf.dart';
 
 import 'widgets/action_button.dart';
 import 'package:sip_ua/sip_ua.dart';
@@ -272,9 +270,6 @@ class _MyCallScreenWidget extends State<CallScreenWidget>
 
   void _handleDtmf(String tone) {
     print('Dtmf tone => $tone');
-    if (WebRTC.platformIsMobile) {
-      FlutterDtmf.playTone(digits: tone);
-    }
     call.sendDTMF(tone);
   }
 
@@ -490,40 +485,41 @@ class _MyCallScreenWidget extends State<CallScreenWidget>
     }
 
     stackWidgets.addAll([
-      Positioned(
-        top: voiceonly ? 48 : 6,
-        left: 0,
-        right: 0,
-        child: Center(
-            child: Column(
-          crossAxisAlignment: CrossAxisAlignment.center,
-          mainAxisAlignment: MainAxisAlignment.center,
-          children: <Widget>[
-            Center(
-                child: Padding(
-                    padding: const EdgeInsets.all(6),
-                    child: Text(
-                      (voiceonly ? 'VOICE CALL' : 'VIDEO CALL') +
-                          (_hold
-                              ? ' PAUSED BY ${this._holdOriginator.toUpperCase()}'
-                              : ''),
-                      style: TextStyle(fontSize: 24, color: Colors.black54),
-                    ))),
-            Center(
-                child: Padding(
-                    padding: const EdgeInsets.all(6),
-                    child: Text(
-                      '$remote_identity',
-                      style: TextStyle(fontSize: 18, color: Colors.black54),
-                    ))),
-            Center(
-                child: Padding(
-                    padding: const EdgeInsets.all(6),
-                    child: Text(_timeLabel,
-                        style: TextStyle(fontSize: 14, color: Colors.black54))))
-          ],
-        )),
-      ),
+        Positioned(
+          top: voiceonly ? 48 : 6,
+          left: 0,
+          right: 0,
+          child: Center(
+              child: Column(
+            crossAxisAlignment: CrossAxisAlignment.center,
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              Center(
+                  child: Padding(
+                      padding: const EdgeInsets.all(6),
+                      child: Text(
+                        (voiceonly ? 'VOICE CALL' : 'VIDEO CALL') +
+                            (_hold
+                                ? ' PAUSED BY ${this._holdOriginator.toUpperCase()}'
+                                : ''),
+                        style: TextStyle(fontSize: 24, color: Colors.black54),
+                      ))),
+              Center(
+                  child: Padding(
+                      padding: const EdgeInsets.all(6),
+                      child: Text(
+                        '$remote_identity',
+                        style: TextStyle(fontSize: 18, color: Colors.black54),
+                      ))),
+              Center(
+                  child: Padding(
+                      padding: const EdgeInsets.all(6),
+                      child: Text(_timeLabel,
+                          style:
+                              TextStyle(fontSize: 14, color: Colors.black54))))
+            ],
+          )),
+        ),
     ]);
 
     return Stack(