netxen: remove unused firmware exports

Quote from Amit Salecha:

"Actually I was not updated, NX_UNIFIED_ROMIMAGE_NAME (phanfw.bin) is already
submitted and its present in linux-firmware.git.

I will get back to you on NX_P2_MN_ROMIMAGE_NAME, NX_P3_CT_ROMIMAGE_NAME and
NX_P3_MN_ROMIMAGE_NAME. Whether this will be submitted ?"

We have to remove these, otherwise we will get wrong info from modinfo.

Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Amit Kumar Salecha <amit.salecha@qlogic.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Dhananjay Phadke <dhananjay.phadke@qlogic.com>
Cc: Narender Kumar <narender.kumar@qlogic.com>
Acked-by:  Amit Kumar Salecha <amit.salecha@qlogic.com>--
Signed-off-by: David S. Miller <davem@davemloft.net>