[deprecate] Deprecate LightningModule.loaded_optimizer_states_dict

[ananthsub]

What does this PR do?

This is a property on the core LightningModule API, but there are no references to it anywhere else in the project. As a result, I propose deprecating it to clean up the API

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[codecov]

Codecov Report

Merging #8229 (644a8ee) into master (d51b0ae) will decrease coverage by 5%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #8229    +/-   ##
=======================================
- Coverage      93%     88%    -5%     
=======================================
  Files         212     212            
  Lines       13695   13703     +8     
=======================================
- Hits        12735   12060   -675     
- Misses        960    1643   +683     

[Borda]

just removing without any replacement?