Remove version freezing for external content

[capyisslay]

Please confirm the following.

• I checked the existing issues for duplicate feature requests

What parts of Modrinth is your feature request related too?

Modrinth App

Is your suggested feature related to a problem? Please describe.

Freezing a version for external content is unnecesary, since it can't be changed anyway.

Describe the solution you'd like

Remove the button for freezing the version for external content

Describe alternatives you've considered

Make the "freeze version" button grayed out (unclickable)

Additional context

No response