During reset/shutdown, clean up leases in DIX instead of each driver

Instead of having every video driver loop over any pending leases to
free them during CloseScreen, do this up in the DIX layer by
terminating leases when a leased CRTC or Output is destroyed and
(just to make sure), also terminating leases in RRCloseScreen. The
latter should "never" get invoked as any lease should be associated
with a resource which was destroyed.

This is required as by the time the driver's CloseScreen function is
invoked, we've already freed all of the DIX randr structures and no
longer have any way to reference the leases

Signed-off-by: Keith Packard <keithp@keithp.com>
Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=106960
Cc: Thomas Hellstrom <thellstrom@vmware.com>