[Keyboard] Remove RGB_MATRIX_SPLIT_RIGHT from crkbd (#7267)

The need for this was dropped in 947e61eaebf168c0c60be34914141cff9a69e599

keyboards/crkbd/rev1/rules.mk

@@ -1,9 +1,3 @@
-RGB_MATRIX_SPLIT_RIGHT = no  # if no, order LEDs for left hand, if yes, order LEDs for right hand
-
-ifeq ($(strip $(RGB_MATRIX_SPLIT_RIGHT)), yes)
-    OPT_DEFS += -DRGB_MATRIX_SPLIT_RIGHT
-endif
-
 SRC += 	matrix.c \
 		split_util.c \
 		split_scomm.c