Documentation: drop Linux Source Driver from kernel-docs references

Dropping LSD (Linux Source Driver) since it hasn't been available
for a long time.

Signed-off-by: Luis de Bethencourt <luis@debethencourt.com>
Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>