Prevent settings from being announced on wifi dialog.

Since no label was shown, when the wifi dialog was popped up from
within setup wizard, talkback would announce the apk name, settings.
Add an empty label so that the wifi dialog/access point name would
be announced instead only.

bug:27529648
Change-Id: I62187731bb88c51b9426cd07bf03733d677e30b5

AndroidManifest.xml

@@ -2685,6 +2685,7 @@
         </activity>
 
         <activity android:name=".wifi.WifiDialogActivity"
+            android:label=""
             android:theme="@style/Transparent"
             android:excludeFromRecents="true"
             android:exported="true"