docs: ABI: sysfs-class-led-trigger-pattern: remove repeat duplication

As reported by scripts/get_abi.pl:

	Warning: /sys/class/leds/<led>/repeat is defined 2 times:  Documentation/ABI/testing/sysfs-class-led-driver-el15203000:0  Documentation/ABI/testing/sysfs-class-led-trigger-pattern:28

The definition for the EL15203000 is just a special case of
the sysfs led class. So, drop it and mentions the possible
exception at the class definition.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/394580bd2e007ffb640f97212973a772ed8f0409.1621413933.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>