fix: remove unnecessary dependency on libcst and scripts

[HemangChothani]

Fixes#218

[tseaver]

#218 says:

Remove libcst as a dependency and edit the fixup script to raise an error if the library is not installed.

Please restore the scripts, and edit as directed.

[HemangChothani]

@tres I found in bigquery PR , that they deleted the file and enter in exclude in syth.py so followed the same. Please guide the correct way.

[tseaver]

@busunkim96 you specified in #218 that the fix was to remove the dependency, and update the script(s) to raise an error if libcst could not be imported. Please clarify.

[HemangChothani]

@busunkim96 Could you please give some clarification?

[crwilcox]

I can weigh in here also. the script has value, but libcst is only needed for the script. We shouldn't list it in our dependencies. Instead, we should import it, catch the import error, and end the script with a message explaining the user should python -m pip install "libcst >= 0.2.5"

@tswast was the script not useful for bigquery by chance?

[tswast]

was the script not useful for bigquery by chance?

Correct. It was useless for BigQuery since we wrap the client objects in the BigQuery Storage API and in the core library we don't use the client objects at all. We only need the generator to make the compiled protos in the core library.

Still, I think it makes sense to make libcst an optional dependency, as it conflicts with the awssdk library due to incompatible YAML version requirements.