IB/usnic: Remove unused prototype

query_protocol() was added in commit 6b90a6d6 ("IB/Verbs:
Implement new callback query_protocol()") and then removed in
commit f9b22e35 ("IB/core: Convert core to use bitfield
for caps").

This left behind an unused prototype.

Signed-off-by: Nelson Escobar <neescoba@cisco.com>
Reviewed-by: Dave Goodell <dgoodell@cisco.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>