cursor: remove strict focus-follows-cursor mode

This is pretty much unusable after recent improvements to the cursor
code, and was totally broken causing a stack overflow as soon as the
cursor was moved over any surface until the previous commit.

Furthermore, none of the core contributors or people active on IRC seem
to use it.

doc/riverctl.1.scd

@@ -242,16 +242,14 @@ A complete list may be found in _/usr/include/linux/input-event-codes.h_
 *border-width* _pixels_
 	Set the border width to _pixels_.
 
-*focus-follows-cursor* *disabled*|*normal*|*strict*
-	There are three available modes:
+*focus-follows-cursor* *disabled*|*normal*
+	There are two available modes:
 
 	- _disabled_: Moving the cursor does not affect focus. This is
 	  the default.
 	- _normal_: Moving the cursor over a view will focus that view.
 	  Moving the cursor within a view will not re-focus that view if
 	  focus has moved elsewhere.
-	- _strict_: Moving the cursor over a view or within a view will
-	  focus that view.
 
 	If the view to be focused is on an output that does not have focus,
 	focus is switched to that output.