chore(conda): remove main channel

[vringar]

By using the conda-forge channel exclusively we should get the most up-to-date software

See #1111 for the second commit

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 38.44%. Comparing base (dedc84b) to head (adbbbc4).
Report is 8 commits behind head on master.

❗ There is a different number of reports uploaded between BASE (dedc84b) and HEAD (adbbbc4). Click for more details.

HEAD has 15 uploads less than BASE

Flag	BASE (dedc84b)	HEAD (adbbbc4)
	17	2

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1110      +/-   ##
==========================================
- Coverage   45.64%   38.44%   -7.20%     
==========================================
  Files          35       35              
  Lines        3475     3475              
==========================================
- Hits         1586     1336     -250     
- Misses       1889     2139     +250     

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