fix: Use version.py instead of pkg_resources on v1

[kyohei3]

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Fixes #1670 🦕

[kyohei3]

Kokoro has been Expected — Waiting for status to be reported status for 10 hours...
Trying to refresh the status by changing base branch temporally, but I'm not sure if a new build was triggered successfully.

[kyohei3]

hmm, kokoro was not triggered yet. will try to close and re-open this pr.