kitty: Remove LF properly

This is an addendum to 278b0c8.

Unfortunately cutting the while loop short is not enough, because stl is
still referenced in its entirety (e.g. with string suffix constructions)
many times inside the loop.

Instead of carefully adjusting each index, we just remove the LF at the
start now.

Author: vimpostor

doc/tpipeline-kitty.txt

@@ -49,9 +49,10 @@ from kitty.utils import color_as_int
 timer_id = None
 
 def parse_stl(screen: Screen, draw_data: DrawData, stl: str, draw: bool):
+	stl = stl[:-1] # remove LF
 	pos = 0
 	length = 0
-	while pos < len(stl) - 1:
+	while pos < len(stl):
 		next = stl.find("#[", pos)
 		if next == -1:
 			length += len(stl[pos:])