Remove constraint variant either

[JSAbrahams]

Relevant issues

Resolves #366 Should make an issue to discuss whether we want to allow different types for arms of match and if expressions: #370

Summary

This was redundant and added unnecessary logic I believe. One problem is that now that the arms of an if expression must always match. One cool feature would be that the language then instead takes a union of these two types and continues on.

Added Tests

• Happy Add test to check assign isn't overridden, more relevant to #364

[codecov[bot]]

Codecov Report

Merging #369 (b5afaeb) into develop (02f25d9) will decrease coverage by 0.17%. The diff coverage is 83.33%.

@@             Coverage Diff             @@
##           develop     #369      +/-   ##
===========================================
- Coverage    87.07%   86.89%   -0.18%     
===========================================
  Files          108      108              
  Lines        11965    11958       -7     
===========================================
- Hits         10418    10391      -27     
- Misses        1547     1567      +20     

[JSAbrahams]

Well, the reduction is coverage is unfortunate. But not much we can do about it in this PR I think.