remove deprecated functions from available_ppc()

[jgabry]

closes #339

Removes ppc_loo_pit() from available_ppc() since it's deprecated. I think that's the only one we need to remove for now.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.62%. Comparing base (7f45740) to head (0de7c85).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #340   +/-   ##
=======================================
  Coverage   98.62%   98.62%           
=======================================
  Files          35       35           
  Lines        5464     5465    +1     
=======================================
+ Hits         5389     5390    +1     
  Misses         75       75           

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