Remove mmap support

[keithbennett]

In GitLab by Keith Bennett (@keithbennett) on 30 Jul 2017, 14:52 (GitLab issue GL#28)

Since arrays are now read-on-demand, there is no longer a compelling reason for using mmap regions. They are complicated and introduce compiler optimisation bugs.

[keithbennett]

In GitLab by Keith Bennett (@keithbennett) on 24 Apr 2018, 16:36

The mmap option was removed from the python reader with MR SDF/SDF_utilities!12
It has yet to be removed from the C-library