fix setup call while testing

[rohitgr7]

What does this PR do?

Fixes #2620

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[codecov]

Codecov Report

Merging #2624 into master will decrease coverage by 0%.
The diff coverage is 86%.

@@          Coverage Diff           @@
##           master   #2624   +/-   ##
======================================
- Coverage      91%     91%   -0%     
======================================
  Files          70      70           
  Lines        5778    5776    -2     
======================================
- Hits         5270    5268    -2     
  Misses        508     508           

[jeremyjordan]

A couple things:

• This removes the check to see if a model has implemented setup. I think it should be ok since the base class method is a no-op, but let's verify this with @williamFalcon since he wrote that line.
• Could you an a test which explicitly checks for the bug mentioned in Only invoke setup() once, not in both trainer.fit() and trainer.test() #2620 so we can prevent future regressions?

[mergify]

This pull request is now in conflict... :(