Fix AdminInterface Inheritance

[VincentLanglet]

Subject

When working on merge 3.x into master, I had to make this change because the signature wasn't compatible.
The issue didn't appear on 3.x because we were just using @method.

I am targeting this branch, because I consider this as a bug fix.

But I have some questions (cc @wbloszyk)

• Shouldn't MutableTemplateRegistryAwareInterface extends TemplateRegistryAwareInterface this way ?

interface MutableTemplateRegistryAwareInterface extends TemplateRegistryAwareInterface
{
    /**
     * @return MutableTemplateRegistryInterface
     */
    public function getTemplateRegistry(): TemplateRegistryInterface;

    /**
     * @param TemplateRegistryInterface
     */
    public function setTemplateRegistry(TemplateRegistryInterface $templateRegistry): void;
}

• The TemplateRegistryAwareInterface is not used at all after this change. Is it useful to keep it ?

Changelog

### Fixed
- `AdminInterface` extends `MutableTemplateRegistryAwareInterface` instead of `TemplateRegistryAwareInterface`

[wbloszyk]

MutableTemplateRegistryAwareInterface and TemplateRegistryAwareInterface are diffrence. They will be used to auto generate template registry, so we should keep both.

First interface should be used in AbstractAdmin.
Second should be used in Pool (in 4.0).