Remove GH workflow and actions to generate documentation

[aulorbe]

Problem

We tried a variety of different solutions for pushing static documentation to our GH pages site (see sdk-docs repo for more information), but the rendering was very bad.

Related PRs:

• Add GH action to push Godoc documentation to sdk-docs repo #41
• Adjust build-docs/action to make /docs dir if it doesn't exist #42
• Add GH action + workflow for setting up Go env in CI #43
• Fix incorrect path in action.yml #44
• Try new strategy for better rendering of documentation with gopages #45
• Change dir in documentation GH action to contain multiple HTML pages #46

Solution

• Simply use the default hosting site of pkg.go.dev, and include instructions for visiting the documentation on main vs the latest release-version's documentation.
• Changed the documentation badge to point to latest documentation on main instead of latest versioned-release's documentation.
• Remove GH workflow and action files

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)

[aulorbe]

Just updated this while I was in there -- it's the latest action

[aulorbe]

This auto-resolves to the latest release

[aulorbe]

@main here points at the main branch

[austin-denoble]

Really appreciate the diligence here, thank you Audrey!