Raise ValueError instead of asserts in src/transformers/benchmark/benchmark.py
Author: AkechiShiro
Pull request: yes

# What does this PR do?

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Replaced all asserts statements by raising `ValueError` exception in `src/transformers/benchmark/benchmark.py`

Related to issue : #12789 

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I'm tagging @patrickvonplaten since he is in charge of the benchmark library. 

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Models:

- albert, bert, xlm: @LysandreJik
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Comments:
Perhaps this could be extended to the library in general? There are still many assert statements in place where Exceptions are more appropriate. Almost all assert statements in the core codebase would be more appropriate as Exceptions - particularly in light of Python's -O and -OO flags.