Remove obsolete files and deprecated code

[marcpaterno]

Description

This PR removes much deprecated code. The code had been deprecated since v1.8; we are removing it in v1.10.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

The following checklist will make sure that you are following the code style and
guidelines of the project as described in the
contributing page.

• I have run bash pre-commit-check and fixed any issues
• I have added tests that prove my fix is effective or that my feature works
• I have made corresponding changes to the documentation
• I have 100% test coverage for my changes (please check this after the CI system has verified the coverage)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.0%. Comparing base (6095a34) to head (217ff36).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #493   +/-   ##
=======================================
  Coverage   100.0%   100.0%           
=======================================
  Files          55       45   -10     
  Lines        4329     4260   -69     
  Branches      468      466    -2     
=======================================
- Hits         4329     4260   -69     

Files with missing lines	Coverage Δ
...recrown/likelihood/binned_cluster_number_counts.py	100.0% <ø> (ø)
firecrown/likelihood/gaussfamily.py	100.0% <ø> (ø)
firecrown/likelihood/gaussian.py	100.0% <ø> (ø)
firecrown/likelihood/number_counts.py	100.0% <ø> (ø)
firecrown/likelihood/source.py	100.0% <ø> (ø)
firecrown/likelihood/student_t.py	100.0% <ø> (ø)
firecrown/likelihood/supernova.py	100.0% <ø> (ø)
firecrown/likelihood/two_point.py	100.0% <ø> (ø)
firecrown/likelihood/weak_lensing.py	100.0% <ø> (ø)
firecrown/parameters.py	100.0% <100.0%> (ø)