Revert systemui status bar provider model behavior

This CL reverts the status bar provider model behavior. It removes the
logic to show only one icon at a time, and removes showing the call
strength indicators.

This change keeps the Internet tile, and decouples SystemUI from the
system setting SETTING_PROVIDER_MODEL.

Bug: 191903788
Test: atest SystemUITests SystemUIGoogleTests; manual
Test: test with a SIM and a Wi-Fi connection and there should be both
      icons in the status bar and quick settings with this change. As
      well as the Internet tile should stay (rather than going back to
      the Cell and Wi-Fi tiles).
Change-Id: I017c10e4d7c1b15b152c44d092695dbc77e4a0ec