zasm: don't accept "0X" prefix for hex anymore

This was only necessary in the time where input was upcased right after
reading.

apps/zasm/parse_z.asm

@@ -102,9 +102,6 @@ hasHexPrefix:
 	inc	hl
 	ld	a, (hl)
 	cp	'x'
-	jr	z, .end
-	cp	'X'
-.end:
 	pop	hl
 	ret