Remove unused density profile coefficients objects

[EmilyBourne]

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[julianlitz]

I didn't fully review everything but the idea is correct.

In Take we use [] anyways so domain_geometry. or density_profile. isn't used.

In Give we retrieve all values via the level_cache class which manages this automatically for us.

Thus these objects can be removed from the multigrid operators.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.31%. Comparing base (f65947b) to head (7944545).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #199   +/-   ##
=======================================
  Coverage   95.31%   95.31%           
=======================================
  Files          86       86           
  Lines        9469     9393   -76     
=======================================
- Hits         9025     8953   -72     
+ Misses        444      440    -4     

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