IB/core: Remove unimplemented ib_peek_cq

IB/core: Remove unimplemented ib_peek_cq

ib_peek_cq() verb doesn't seem be implemented in current code.
There is some past reference to it at [1] about it being unimplemented.

Lot of user documentation created out of kdoc refers to this
unimplemented API. Therefore, remove unimplemented API.

[1] http://lists.openfabrics.org/pipermail/ofw/2008-May/002465.html
Signed-off-by: Parav Pandit <parav@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>