MAINT: integrate apmpi and apss modules from autoperf directly into the Darshan source tree

[carns]

Not urgent; this can be done after 3.5.0.

Currently the autoperf code is maintained in a separate repository at https://github.com/argonne-lcf/autoperf/. It is then included in Darshan using a git submodule and optionally configured and built if present.

There are two parts of autoperf that are potentially relevant and worth maintaining:

• apss: collects Slingshot network topology information a startup/shutdown using PAPI. This may be interesting data to have, and would be very lightweight to capture since it doesn't interfere with anything during execution.
• apmpi: collects statistics about general MPI usage (not just I/O). This could be useful for some performance studies, but it isn't clear at this point how much overhead it adds. There could be risk to enabling it by default if applications make heavy use of low-latency collectives.

We can leave the existing autoperf repository as is for historical purposes, but do the following in Darshan:

• Get rid of the submodule
• Put apss and apmpi directly in the tree (do not try to preserve git history)
• Disable them by default

This will make them easier to maintain moving forward, and will discard the portions of Autoperf that are no longer relevant.