Disable DDP for neuron
Author: sangeethabal
Pull request: yes

# What does this PR do?
This PR is to disable DDP when using neuron. Currently, we are overwriting the _wrap_model function in trainer.py to disable DDP. We want to avoid overwriting by disabling DDP when using neuron.
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## Before submitting
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## Who can review?
@sgugger

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Comments:
_The documentation is not available anymore as the PR was closed or merged._