🐞 fix(Permission): some Android bug

1，fix 构建QRView时，onPermissionSet函数多次返回。2，fix 销毁QRView时，会展示权限弹窗

https://github.com/juliuscanute/qr_code_scanner/issues/305

android/src/main/kotlin/net/touchcapture/qr/flutterqr/QRView.kt

@@ -102,8 +102,6 @@ class QRView(messenger: BinaryMessenger, id: Int, private val params: HashMap<St
     private fun flipCamera(result: MethodChannel.Result) {
         if (barcodeView == null) {
             return barCodeViewNotSet(result)
-        } else if (!hasCameraPermission()) {
-            checkAndRequestPermission(result)
         } else {
             barcodeView!!.pause()
             val settings = barcodeView!!.cameraSettings
@@ -146,8 +144,6 @@ class QRView(messenger: BinaryMessenger, id: Int, private val params: HashMap<St
     private fun pauseCamera(result: MethodChannel.Result) {
         if (barcodeView == null) {
             return barCodeViewNotSet(result)
-        } else if (!hasCameraPermission()) {
-            checkAndRequestPermission(result)
         } else {
             if (barcodeView!!.isPreviewActive) {
                 isPaused = true
@@ -160,8 +156,6 @@ class QRView(messenger: BinaryMessenger, id: Int, private val params: HashMap<St
     private fun resumeCamera(result: MethodChannel.Result) {
         if (barcodeView == null) {
             return barCodeViewNotSet(result)
-        } else if (!hasCameraPermission()) {
-            checkAndRequestPermission(result)
         } else {
             if (!barcodeView!!.isPreviewActive) {
                 isPaused = false
@@ -203,11 +197,7 @@ class QRView(messenger: BinaryMessenger, id: Int, private val params: HashMap<St
                 barcodeView?.cameraSettings?.requestedCameraId = CameraInfo.CAMERA_FACING_FRONT
             }
         } else {
-            if (hasCameraPermission()) {
-                if (!isPaused) barcodeView!!.resume()
-            } else {
-                checkAndRequestPermission(null)
-            }
+            if (!isPaused) barcodeView!!.resume()
         }
         return barcodeView
     }