Don't show welcome screen when talkback is on and on pre-L-MR1

- This is a workaround.

Bug: 31180524

Test: manual - welcome screen is not shown if we are on Lollipop
               and Talkbak is on.

Change-Id: I02636d2d5f305b9d0281f5a6cce88af79573b847
1 file changed