Remove redundant require_backward_grad_sync=False in sharded plugins

[awaelchli]

What does this PR do?

Attempt to remove redundant setattr(model, "require_backward_grad_sync", False) call in sharded plugins.
Addresses comment in #10028 (comment)

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[github-actions]

Build Error! No Linked Issue found. Please link an issue or mention it in the body using #<issue_id>

[four4fish]

Thank you for addressing this in a different PR

[codecov]

Codecov Report

Merging #10065 (7020bdb) into master (c3614f1) will decrease coverage by 0%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #10065   +/-   ##
=======================================
- Coverage      92%      92%   -0%     
=======================================
  Files         182      182           
  Lines       16113    16111    -2     
=======================================
- Hits        14896    14894    -2     
  Misses       1217     1217