chore: Remove Python from final image since it is only used to convert keras to tensorflow

[GolanLevy]

... which we may not need, hence reducing the image size from 2.14Gb to 256Mb

#59

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[ckadner]

@GolanLevy -- I see you closed this PR. Your criticism has merit though. Maybe we could introduce another build stage to install the conversion script, but only copy the minimally required python packages into the final minimal image?

[GolanLevy]

@ckadner I opened this PR by mistake (wanted to test it first on my repo, which worked btw).
Before implementing any special logic, I suggest to revise the original need for the conversion script. If we decide that the script is unnecessary, we can just eliminate it and all the python packages.
The conversion script converts model at runtime. Why is it necessary? This should not be handled as part of a production flow imo.
If a user has a Keras model, encourage him to preprocess the model (using the script) prior to serving it.