nvmet-fc: Remove unused functions

The functions nvmet_fc_iodnum() and nvmet_fc_fodnum() are currently
unutilized.

Following commit c5343203 ("nvme-fabrics: Add target support for FC
transport"), which introduced these two functions, they have not been
used at all in practice.

Remove them to resolve the compiler warnings.

Fix follow errors with clang-19 when W=1e:
  drivers/nvme/target/fc.c:177:1: error: unused function 'nvmet_fc_iodnum' [-Werror,-Wunused-function]
    177 | nvmet_fc_iodnum(struct nvmet_fc_ls_iod *iodptr)
        | ^~~~~~~~~~~~~~~
  drivers/nvme/target/fc.c:183:1: error: unused function 'nvmet_fc_fodnum' [-Werror,-Wunused-function]
    183 | nvmet_fc_fodnum(struct nvmet_fc_fcp_iod *fodptr)
        | ^~~~~~~~~~~~~~~
  2 errors generated.
  make[8]: *** [scripts/Makefile.build:207: drivers/nvme/target/fc.o] Error 1
  make[7]: *** [scripts/Makefile.build:465: drivers/nvme/target] Error 2
  make[6]: *** [scripts/Makefile.build:465: drivers/nvme] Error 2
  make[6]: *** Waiting for unfinished jobs....

Fixes: c5343203 ("nvme-fabrics: Add target support for FC transport")
Signed-off-by: WangYuli <wangyuli@uniontech.com>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>