Remove coding: utf-8 from python files as that's the default already for python 3

cc @cbornet (2017/09) @tomplus (2018/10) @krjakbrjak (2023/02) @fa0311 (2023/10) @multani (2023/10)

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Summary by cubic

Remove unnecessary "# coding: utf-8" headers from Python templates and generated clients, since UTF-8 is the default in Python 3. This cleans up files with no behavior change.

• Refactors
  • Removed encoding headers from python/*.mustache, including setup.mustache
  • Regenerated Python sample clients to reflect the change

^{Written for commit 7b8e544. Summary will update on new commits.}