Container Registry UI: remove the repository importing error support

🔥 Problem

In !82730 (merged), we added frontend support for the repository importing error that could happen when users try to destroy tags.

Once it's confirmed that repository importing errors can't happen any more, that support code will be dead / unreachable code.

🚒 Solution

• Remove the support of the repository importing error

Implementation guide

• Revert frontend changes added in Update error message with an importing containe... (!82730 - merged)