Remove redundant function get_cat

[mwcraig]

Closes #96 by replacing get_cat with a call to apass_dr9.

[codecov-commenter]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (a222f49) 53.66% compared to head (d35a332) 53.80%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
stellarphot/utils/magnitude_transforms.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #230      +/-   ##
==========================================
+ Coverage   53.66%   53.80%   +0.13%     
==========================================
  Files          23       23              
  Lines        2890     2881       -9     
==========================================
- Hits         1551     1550       -1     
+ Misses       1339     1331       -8     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.