Documentation: Remove "ltpc=" from the kernel-parameters.txt

Documentation: Remove "ltpc=" from the kernel-parameters.txt

The string "ltpc" cannot be found in the source code anymore. This
kernel parameter likely belonged to the LocalTalk PC card module
which has been removed in commit 03dcb90dbf62 ("net: appletalk:
remove Apple/Farallon LocalTalk PC support"), so we should remove
it from kernel-parameters.txt now, too.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240614084633.560069-1-thuth@redhat.com