registers: remove obsolete comment

[gudnimg]

The registers were moved into program memory in FW 3.0.1

See for reference the relevant pull request:
#287

[github-actions]

All values in bytes. Δ Delta to base

ΔFlash	ΔSRAM	Used Flash	Used SRAM	Free Flash	Free SRAM
0	0	28132	1667	540	893

[github-actions]

Automated Test Code Coverage Report

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File	Lines	Exec	Cover
src/application.cpp	169	14	8%
src/application.h	3	3	100%
src/hal/circular_buffer.h	52	52	100%
src/hal/eeprom.h	1	0	0%
src/hal/gpio.h	18	7	38%
src/hal/progmem.h	6	6	100%
src/hal/tmc2130.cpp	113	9	7%
src/hal/tmc2130.h	31	27	87%
src/logic/command_base.cpp	139	118	84%
src/logic/command_base.h	4	3	75%
src/logic/cut_filament.cpp	117	80	68%
src/logic/eject_filament.cpp	77	60	77%
src/logic/feed_to_bondtech.cpp	60	57	95%
src/logic/feed_to_bondtech.h	1	1	100%
src/logic/feed_to_finda.cpp	48	45	93%
src/logic/feed_to_finda.h	1	1	100%
src/logic/home.cpp	18	12	66%
src/logic/load_filament.cpp	85	77	90%
src/logic/load_filament.h	1	0	0%
src/logic/move_selector.cpp	21	0	0%
src/logic/no_command.h	2	1	50%
src/logic/retract_from_finda.cpp	27	21	77%
src/logic/retract_from_finda.h	1	1	100%
src/logic/set_mode.cpp	5	0	0%
src/logic/set_mode.h	1	0	0%
src/logic/start_up.cpp	38	26	68%
src/logic/start_up.h	4	4	100%
src/logic/tool_change.cpp	108	82	75%
src/logic/unload_filament.cpp	76	69	90%
src/logic/unload_to_finda.cpp	40	39	97%
src/logic/unload_to_finda.h	1	1	100%
src/modules/axisunit.h	21	21	100%
src/modules/buttons.cpp	11	11	100%
src/modules/buttons.h	7	7	100%
src/modules/crc.h	13	13	100%
src/modules/debouncer.cpp	28	24	85%
src/modules/debouncer.h	7	7	100%
src/modules/finda.cpp	7	3	42%
src/modules/finda.h	2	2	100%
src/modules/fsensor.cpp	6	6	100%
src/modules/fsensor.h	3	3	100%
src/modules/globals.cpp	47	42	89%
src/modules/globals.h	34	24	70%
src/modules/idler.cpp	89	82	92%
src/modules/idler.h	12	12	100%
src/modules/leds.cpp	44	42	95%
src/modules/leds.h	16	15	93%
src/modules/math.h	6	6	100%
src/modules/motion.cpp	59	40	67%
src/modules/motion.h	66	64	96%
src/modules/movable_base.cpp	73	70	95%
src/modules/movable_base.h	16	16	100%
src/modules/permanent_storage.cpp	144	89	61%
src/modules/protocol.cpp	216	184	85%
src/modules/protocol.h	72	70	97%
src/modules/pulley.cpp	33	25	75%
src/modules/pulley.h	8	5	62%
src/modules/pulse_gen.cpp	95	89	93%
src/modules/pulse_gen.h	53	51	96%
src/modules/selector.cpp	69	62	89%
src/modules/selector.h	5	5	100%
src/modules/speed_table.h	26	24	92%
src/modules/user_input.cpp	39	39	100%
src/modules/user_input.h	12	12	100%
src/modules/voltage.cpp	4	0	0%
src/registers.cpp	104	37	35%
src/unit.h	12	12	100%
TOTAL	2727	2030	74%

TOTAL: 2727 lines of code, 2030 lines executed, 74% covered.