Screen magnification cannot be engaged in landscape on a phone.

1. The reason is that the screen magnifier computes that the whole
   screen is not magnifiable. The miscalculation was caused due to
   an incorrect assumption that the non-magnified area is only at
   the bottom. In fact, on a phone in landscape the non-magnified
   area is both on the right and at the bottom. This change adds
   a correct algorithm for computing the magnified region.

2. Increasing the delay for computing the magnified area when the
   keyguard goes away to allow all windows hidden by the keyguard
   to be shown. In rare occasions the previous delay was not long
   enough resulting in a state where the keyboard is considered
   a part of the magnified region.

3. Removed some dead code.

bug:7293097

Change-Id: Ic5ff91977df8bcf4afd77071685c3eb20555d4f3