Remove deprecated on_init_start_end

[AndresAlgaba]

What does this PR do?

Removes deprecated APIs for 1.8 release, #14841. More specifically, the removal of test_v1_8_0_on_init_start_end.

resolves #10940

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Make sure you had fun coding 🙃

[awaelchli]

@AndresAlgaba I saw your message earlier and if you have trouble running the tests let me know. You can also check the output of the CI here, for example Test PyTorch full / pl-cpu (ubuntu-20.04, 3.10, latest, stable). There may be some jobs failing that are unrelated to your PR.

[awaelchli]

Looks great @AndresAlgaba
Feel free to mark the PR as ready for review 😃

[krishnakalyan3]

great work @AndresAlgaba

[codecov]

Codecov Report

Merging #14867 (2357cf2) into master (abea29b) will increase coverage by 1%.
The diff coverage is n/a.

❗ Current head 2357cf2 differs from pull request most recent head e9ee5fc. Consider uploading reports for the commit e9ee5fc to get more accurate results

Additional details and impacted files

@@            Coverage Diff            @@
##           master   #14867     +/-   ##
=========================================
+ Coverage      83%      84%     +1%     
=========================================
  Files         395      327     -68     
  Lines       28832    25513   -3319     
=========================================
- Hits        23902    21371   -2531     
+ Misses       4930     4142    -788