chore: remove obsolete replacement in owlbot.py

[parthea]

This PR removes a replacement in owlbot.py which is obsolete

Here are the commands that I used to validate the change

• In a clone of googleapis/googleapis, run

bazel build //google/cloud/assuredworkloads/v1:assuredworkloads-v1-py
bazel build //google/cloud/assuredworkloads/v1beta1:assuredworkloads-v1beta1-py

• In this branch, run owlbot copy code and the owlbot post processor

docker run --rm --user $(id -u):$(id -g)   -v $(pwd):/repo   -v $HOME/git/googleapis/bazel-bin:/bazel-bin   gcr.io/cloud-devrel-public-resources/owlbot-cli:latest copy-bazel-bin   --source-dir /bazel-bin --dest /repo

docker run --user $(id -u):$(id -g) --rm -v $(pwd):/repo -w /repo gcr.io/cloud-devrel-public-resources/owlbot-python:latest

[parthea]

Wait for googleapis/gapic-generator-python#1645 and googleapis/gapic-generator-python#1646