e1000: remove broken support for 82573L

e1000: remove broken support for 82573L

Currently, e1000 support is based on the manual for the 8254xx
model series. 82573x models are documented in a separate manual
(see http://www.intel.com/content/dam/www/public/us/en/documents/manuals/pcie-gbe-controllers-open-source-manual.pdf)
and the 82573L device ID no longer works correctly on either Linux
(3.14.*) or Windows 7.

This patch removes stale code claiming to support 82573L, cleaning
up the code base for the remaining 8254xx model series.

Signed-off-by: Gabriel Somlo <somlo@cmu.edu>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>