3/ Update OneHanded to use shell main thread

- Clean up some usages of handlers and explicit main loopers to use
  the shell executors
- Remove the update thread (will eventually move to the shell main thread)
- Make timeout handler non-static (it only has one instance at the moment)
- Post calls from shell back onto the sysui thread

Bug: 161979899
Test: atest WMShellUnitTests
Change-Id: I1db0f0d8e7f83eeb7e4581fb266ffd77aa73fea1