Remove stale "depends on NETDEV_1000"in staging drivers

Mark Einon points out that the Kconfig option for NETDEV_1000 no longer
exists, and the merge of the staging drivers should have removed that
for the et131x driver.

And while checking for it, I noticed that slicoss had the same stale
dependency.  Remove that one too.

Reported-by: Mark Einon <mark.einon@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>