chore: use default owlbot.py file

[parthea]

I ran the following commands locally and there were no changes to the generated code.

In a clone of googleapis/googleapis, run these commands to generate the clients

bazel build //google/cloud/documentai/v1:documentai-v1-py
bazel build //google/cloud/documentai/v1beta2:documentai-v1beta2-py
bazel build //google/cloud/documentai/v1beta3:documentai-v1beta3-py

In a clone of this repo, run these commands to copy the generated client and run the 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