Remove deprecated method related with src/Admin/SharedBlockAdmin

[eerison]

Subject

I am targeting this branch, because {reason}.

Closes #{put_issue_number_here}.

Changelog

### Added
- Added some `Class::newMethod()` to do great stuff.

### Changed

### Deprecated

### Removed

### Fixed

### Security

[eerison]

Hey @VincentLanglet do you have any idea, how SharedBlockAdmin defines baseRoutePattern ?

I didn't find out here it's set!

[VincentLanglet]

See #1417 (comment). This will be done directly when bumping sonata to 4.x.

But we need sonata-project/SonataAdminBundle#7867 first

[eerison]

After sonata-project/SonataAdminBundle#7867 pass I'll check if this PR is useful yet.