liquidio: remove unused IQ_INSTR_MODE_64B function

clang with W=1 reports
drivers/net/ethernet/cavium/liquidio/request_manager.c:43:19: error:
  unused function 'IQ_INSTR_MODE_64B' [-Werror,-Wunused-function]
static inline int IQ_INSTR_MODE_64B(struct octeon_device *oct, int iq_no)
                  ^
This function and its macro wrapper are not used, so remove them.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Link: https://lore.kernel.org/r/20230321184811.1827306-1-trix@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>