Deprecate LightningDistributed and keep logic in ddp/ddpSpawn directly

[four4fish]

What does this PR do?

LightningDistributed() class only used by ddp and ddpSpawn, and only have one broadcast function for torch collectives. It's unnecessary to have.
Also, we have to set rank and device in set up steps. If subclass extend DDP or DDPSpawn, and overridden function where LightningDistributed.rank and device setted, could cause silent failures.

Now the src is not respected in torch broadcast, fix the issue

Fixes #9692

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[awaelchli]

Have a look at the tests/deprecated_api where we should add a quick test for the 1.7 removal :)

[codecov]

Codecov Report

Merging #9691 (a7f74d1) into master (8fcdcb5) will decrease coverage by 4%.
The diff coverage is 67%.

❗ Current head a7f74d1 differs from pull request most recent head db5e4e3. Consider uploading reports for the commit db5e4e3 to get more accurate results

@@           Coverage Diff           @@
##           master   #9691    +/-   ##
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- Coverage      93%     89%    -4%     
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  Files         179     178     -1     
  Lines       15306   15297     -9     
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- Hits        14201   13576   -625     
- Misses       1105    1721   +616     

[ananthsub]

i think there's an optimization opportunity for broadcast but we can pick it up in a follow up PR along with tensor specializations