IB/ipath: Remove ipath_layer dead code

The ipath_layer.[ch] code was an attempt to provide a single interface
for the ipath verbs and ipath_ether code to use.  As verbs
functionality increased, the layer's functionality became insufficient
and the verbs code broke away to interface directly to the driver.
The failed attempt to get ipath_ether upstream was the final nail in
the coffin and now it sits quietly in a dark kernel.org corner waiting
for someone to notice the smell and send it along to it's final
resting place.  Roland Dreier was that someone -- this patch expands
on his work...

Signed-off-by: Arthur Jones <arthur.jones@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>