Remove cruft related to window switcher and keyboard focus

Remove cruft related to window switcher and keyboard focus

This commit cleans up the comments and cruft from e45fe08.

Background:

- With e45fe08, the keyboard focus is always moved to the switched window
  on finishing window switcher, even with <focus followMouse="yes">.
  Since followMouseRequiresMovement was not implemented at that time
  (behaved like it was always "no"), e45fe08 was necessary to allow users
  users who use followMouse="yes" to move the keyboard focus with window
  switcher.
- 9a9e20d added followMouseRequiresMovement, but it kept the behavior
  described above even with followMouse="yes" and
  followMouseRequiresMovement="no".
- 398b80b accidentally invalidated e45fe08, which means the keyboard focus
  is now always moved to the window below the cursor on finishing window
  switcher with followMouse="yes" and followMouseRequiresMovement="no".

Although the invalidation was a accident, I think always setting the
keyboard focus on the window below the cursor is what users expect from
followMouse="yes" and followMouseRequiresMovement="no".