Remove WifiSetupActivity

That activity was copied into setup wizard and is no longer used.

Also removed setup_illustration_lock_screen because that is also
not used in the current GLIF theme.

Test: Existing Robolectric tests pass
Bug: 33590605
Change-Id: Ib2ea02a5e4bce17a7ea829b854f73caf7d5c5f97