can: Kconfig: remove obsolete help text for slcan

Commit cfcb4465 ("can: slcan: remove legacy infrastructure")
removed the 10-device limit.  Update the Kconfig help text accordingly.

Signed-off-by: Mans Rullgard <mans@mansr.com>
Acked-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://lore.kernel.org/all/20240427152648.25434-1-mans@mansr.com


Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>