IB/ipath: Remove dead code for user process waiting for send buffer

At one point in time there was code to allow a user process to
wait for a send buffer if none were available. This feature was
never used and most of the code was removed. This removes
some missed unused code.

Signed-off-by: Ralph Campbell <ralph.campbell@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>