Add helper to delete LCE from capsule

[vsedmik]

Description of changes

Adds helper to disassociate lifecycle environment from a capsule

Upstream API documentation, plugin, or feature links

/apidoc/v2/capsule_content.en.html

Functional demonstration

$ pytest tests/foreman/api/test_capsulecontent.py::TestCapsuleContentManagement::test_positive_remove_capsule_orphans
=================================================================== test session starts ===================================================================
...
collected 1 item                                                                                                                                          

tests/foreman/api/test_capsulecontent.py .                                                                                                          [100%]

======================================================== 1 passed, 1 warning in 111.38s (0:01:51) =========================================================

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01 🎉

Comparison is base (cfed8c9) 92.18% compared to head (f2523c4) 92.19%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #935      +/-   ##
==========================================
+ Coverage   92.18%   92.19%   +0.01%     
==========================================
  Files           6        6              
  Lines        3031     3037       +6     
==========================================
+ Hits         2794     2800       +6     
  Misses        237      237              

Impacted Files	Coverage Δ
nailgun/entities.py	91.24% <100.00%> (+0.02%)	⬆️

☔ View full report in Codecov by Sentry.
📢 Do you have feedback about the report comment? Let us know in this issue.

[sambible]

Endpoint seems good, but you should at least update the GenericTestCase with the new endpoint

nailgun/tests/test_entities.py

Line 2105 in cfed8c9

class GenericTestCase(TestCase):

[sambible]

lgtm