feat: remove UpgradeButton

[MaxFrank13]

This removes the UpgradeButton component (#438):

• UpgradeButton is no longer the default content in the CourseCardActionSlot,
• Removes defintion and test files (ie. UpgradeButton.(test.)jsx)
• Removes tracking functions and any other logging utilities specific to the UpgradeButton, including event names and onClick callbacks

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.72%. Comparing base (ce595d0) to head (9bded0a).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #536      +/-   ##
==========================================
- Coverage   97.39%   96.72%   -0.68%     
==========================================
  Files         155      155              
  Lines        1384     1372      -12     
  Branches      232      229       -3     
==========================================
- Hits         1348     1327      -21     
- Misses         34       43       +9     
  Partials        2        2              

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[jsnwesson]

canUpgrade seems to be closely tied to the whole Upgrade button logic and isn't being referenced in any of the other tests in this file. Is it possible that that hook can be removed in this PR as well?

[MaxFrank13]

canUpgrade is still being used by the CourseBanner component (source). There is an internal ticket in our backlog for replacing this with a PluginSlot implementation (source).

However, I think it's references can be removed in this test file! So I'll go ahead and do that

[jsnwesson]

Approved!