Crawling buffs (#4657)

# About the pull request

Makes crawling do_after(how long it takes to crawl to a new tile) 1
second instead of 3 and removes the busy icon.

# Explain why it's good for the game

Its fun, crawling has essentially no use and this makes it a bit better
at potentially hiding in piles of corpses and moving around stealthily,
still useless in actual normal gameplay though.


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:
balance: Crawling now only takes 1 second to move and no longer has an
overhead icon when doing it.
/:cl:

code/modules/mob/mob_movement.dm

@@ -187,7 +187,7 @@
 					return
 			//now crawl
 			mob.crawling = TRUE
-			if(!do_after(mob, 3 SECONDS, INTERRUPT_MOVED|INTERRUPT_UNCONSCIOUS|INTERRUPT_STUNNED|INTERRUPT_RESIST|INTERRUPT_CHANGED_LYING, BUSY_ICON_GENERIC))
+			if(!do_after(mob, 1 SECONDS, INTERRUPT_MOVED|INTERRUPT_UNCONSCIOUS|INTERRUPT_STUNNED|INTERRUPT_RESIST|INTERRUPT_CHANGED_LYING, NO_BUSY_ICON))
 				mob.crawling = FALSE
 				next_movement = world.time + MINIMAL_MOVEMENT_INTERVAL
 				mob.move_intentionally = FALSE