[Fix] Remove DeepSpeed Plugin FP16 exception

[SeanNaren]

What does this PR do?

Removes an exception thrown where the precision isn't set to 16, as this is now supported in Deepspeed.

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[codecov]

Codecov Report

Merging #8462 (92def46) into master (257fabd) will increase coverage by 0%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #8462    +/-   ##
=======================================
  Coverage      92%     92%            
=======================================
  Files         217     217            
  Lines       14097   14221   +124     
=======================================
+ Hits        13004   13126   +122     
- Misses       1093    1095     +2     

[tchaton]

LGTM !