feat(flags): remove Unleash get_variant patching code

[aliu39]

Follow-up to #3888

The original PR patched 2 methods used for evaluating feature flags, is_enabled (simple toggle on/off) and get_variant (returns a dict of metadata, see https://docs.getunleash.io/reference/sdks/python#getting-a-variant).

We want to remove all get_variant code since we only support boolean flag evals atm. It seems like the main usecase for variants is reading payloads (non-bool) for A/B/multivariate testing. This could lead to a lot of extraneous flags, so until it is requested and/or we support non-bool values, let's not patch this method.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 80.16%. Comparing base (288f69a) to head (5bfd873).
Report is 1 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3914      +/-   ##
==========================================
- Coverage   80.20%   80.16%   -0.05%     
==========================================
  Files         139      139              
  Lines       15400    15391       -9     
  Branches     2596     2596              
==========================================
- Hits        12352    12338      -14     
- Misses       2203     2208       +5     
  Partials      845      845              

Files with missing lines	Coverage Δ
sentry_sdk/integrations/unleash.py	90.00% <ø> (-3.11%)	⬇️

... and 1 file with indirect coverage changes

[antonpirker]

less code is good!