Remove ci tpu test from github workflows

[kaushikb11]

What does this PR do?

As we run TPU tests on CircleCI
Fixes #8961

Does your PR introduce any breaking changes? If yes, please list them.

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[codecov]

Codecov Report

Merging #8965 (b1cbe73) into master (522df2b) will decrease coverage by 4%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #8965    +/-   ##
=======================================
- Coverage      93%     89%    -4%     
=======================================
  Files         176     176            
  Lines       14402   14411     +9     
=======================================
- Hits        13343   12772   -571     
- Misses       1059    1639   +580     

[ananthsub]

n00b question: do you know why it was added to GitHub workflows? which tests are supposed to run on CircleCI vs GitHub workflows?

[Borda]

Then you need to run them also on master and edit badge in Readme...

[carmocca]

The README looks good: https://github.com/kaushikb11/pytorch-lightning/tree/remove/ci_test_tpu

[daniellepintz]

What is the status of this pr?