Remove redundant connected notification

Remove the old connected notification since there is a new file
- NetworkStackNotifier.java which will send the connected
notification when captive portal validated.

Bug: 149883761
Test: 1. atest FrameworksNetTests
      2. Sign-in a captive portal and see if there is a redundant
      connected notification.

Change-Id: Id11a9b99dd04772a92af8d527104906c47bf64cd