Remove infiniband polling thread.

src/common/slurm_acct_gather_infiniband.c

src/common/slurm_acct_gather_infiniband.h

...acct_gather_infiniband/none/acct_gather_infiniband_none.c

...acct_gather_infiniband/ofed/acct_gather_infiniband_ofed.c

src/plugins/jobacct_gather/linux/jobacct_gather_linux.c

src/slurmd/slurmstepd/mgr.c