Regenerate bigtable-admin client

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > You are running the synthesis script directly, this will be disabled in a future release of Synthtool. Please use python3 -m synthtool instead.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:2f6b261ee7fe1aedf238991c93a20b3820de37a343d0cacf3e3e9555c2aaf2ea
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/bigtable/admin/artman_bigtableadmin.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/java.
synthtool > Cleaned up 1 temporary directories.

[chingor13]

Combined into a single pull request #4104