Use framework support to reserve icon space

Framework now has iconSpaceReserved attr to support reserving icon
space. We no longer need to use a custom layout for each preference.

What's removed:
- custom style for normal preference
- custom layout/style for dropdown preference
- custom style for EditTextPreference

Fix: 37572422
Test: visual
Change-Id: I48d2997e6269143f58c2edd2d9902cdc0519ed04