drivers/net: delete old 8bit ISA 3c501 driver.

It was amusing that linux was able to make use of this 1980's
technology on machines long past its intended lifespan, but
it probably should go now.

To set some context, the 3c501 was designed in the 1980's to be
used on 8088 PC-XT 8bit ISA machines.  It was built using a large
number of discrete TTL components and truly looks like a relic
of the ancient past before large scale integration was common.

But from a functional point of view, the real issue, as stated
in the (also obsolete) Ethernet-HowTo, is that "...the 3c501 can
only do one thing at a time -- while you are removing one packet
from the single-packet buffer it cannot receive another packet,
nor can it receive a packet while loading a transmit packet."

You know things are not good when the Kconfig help text suggests
you make a cron job doing a ping every minute.

Hardware that old and crippled is simply not going to be used by
anyone in a time where 10 year old 100Mbit PCI cards (that are
still functional) are largely give-away items.

Cc: Alan Cox <alan@linux.intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>