Remove hwloc 1.7.2, no longer needed.

hwloc 1.9 has been the default since June 28, so 1.7.2 can be deleted
now.
Merge pull request #197 from gbtitus/rm-hwloc-1.7

Remove hwloc 1.7.2, no longer needed

[Not reviewed.]

hwloc 1.9 has been the default since June 28, so 1.7.2 can be deleted
now.