Plants don't get their positions ruined when dropped (#58806)

Tiny atomic one line change that makes plants stay in the same place when you drop them.

What's the point of being able to hide in a plant if anyone with basic object permanence can see that a plant that used to be offset off the tile is now centered?
Also I was tired of seeing all the plants in the bar turn really ugly and offset the second Pun Pun gets to them with no way of centering them again.

code/game/objects/structures/flora.dm

@@ -311,6 +311,7 @@
 	throwforce = 13
 	throw_speed = 2
 	throw_range = 4
+	item_flags = NO_PIXEL_RANDOM_DROP
 
 	/// Can this plant be trimmed by someone with TRAIT_BONSAI
 	var/trimmable = TRUE