On a directory page, such as https://pkg.go.dev/github.com/elastic/beats, only these tabs should be enabled:

• Overview
• Subdirectories
• Licenses

At the moment, all of the tabs are enabled, both in the main header and the sticky header.

The logic for which tabs to enable on each page is in internal/frontend/tabs.go.

• On the package page, all tabs should be enabled.
• On the module page overview, packages, versions, and licenses should be enabled.
• On the directory page only licenses, subdirectories, and overview should be enabled.

/cc @andybons