Remove serverless public preview warnings

[austin-denoble]

Problem

The serverless public preview warnings from January are still in docstrings and documentation. Since we've expanded the number of regions available, we should pull these out.

Solution

Remove "public preview" warnings calling out the us-west-2 environment from README, docstrings, and the migration guide.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update
• Infrastructure change (CI configs, etc)
• Non-code change (docs, etc)
• None of the above: (explain here)

Test Plan

CI, run the client reference action after merged to main to update reference docs.

[aulorbe]

lgtm