[dev] [st] bad focus

Hi

Currently, st sets its focus based on both FocusIn and EnterNotify XEvents
and uses this focus to decide whether to draw the cursor. This causes a
problem for window managers that don't use _focus follows pointer_ because
it is then possible for st to have the keyboard focus but not be drawing
the cursor.

The obvious fix is to simply remove the EnterNotify and LeaveNotify events.
I have attached a patch that does so. I've tested this lightly in several
window managers (tiling and non-tiling, various focus models) and it seems
to have the desired effect.

Adrian