[bash] Drop old client.sh from petstore sample

[Fryguy]

The bash config is configured to generate with a scriptName of petstore-cli. As such, it will never generate client.sh and related files. This seems to be a leftover from before the bash config was introduced, and is not needed.

@frol @bkryza @kenjones-cisco

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package || exit
  ./bin/generate-samples.sh ./bin/configs/*.yaml || exit
  ./bin/utils/export_docs_generators.sh || exit
  

  (For Windows users, please run the script in WSL)
  Commit all changed files.
  This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master.
  These must match the expectations made by your contribution.
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