Remove exp_save_path on the LightningModule

[ananthsub]

What does this PR do?

This has no other references inside of lightning today. it looks like this was added in the OG commit for lightning: 2117485

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[codecov]

Codecov Report

Merging #7266 (5750544) into master (b670647) will decrease coverage by 4%.
The diff coverage is n/a.

❗ Current head 5750544 differs from pull request most recent head 94a40fb. Consider uploading reports for the commit 94a40fb to get more accurate results

@@           Coverage Diff           @@
##           master   #7266    +/-   ##
=======================================
- Coverage      91%     87%    -4%     
=======================================
  Files         199     199            
  Lines       12798   12787    -11     
=======================================
- Hits        11679   11121   -558     
- Misses       1119    1666   +547     

[awaelchli]

it's not used anywere so you can just remove it without deprecation right?