chore(python): remove obsolete release scripts and config files

[gcf-owl-bot[bot]]

Source-Link: https://github.com/googleapis/synthtool/commit/635751753776b1a7cabd4dcaa48013a96274372d Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:91d0075c6f2fd6a073a06168feee19fa2a8507692f2519a1dc7de3366d157e99

[parthea]

Superseded by https://github.com/googleapis/python-bigquery-sqlalchemy/pull/1135