Remove redundant code in DefaultEntityCallbacks#callback

[mawen12]

Resolves #3055

I have found org.springframework.data.mapping.callback.DefaultEntityCallbacks#callback method exists redunant code.

entity is checked not null, then don't need to call callbackDiscoverer.resolveDeclaredEntityType(callbackType).getRawClass()).

current code:

@Override
public <T> T callback(Class<? extends EntityCallback> callbackType, T entity, Object... args) {

    Assert.notNull(entity, "Entity must not be null");
    // redunant code 
    Class<T> entityType = (Class<T>) (entity != null ? ClassUtils.getUserClass(entity.getClass())
		: callbackDiscoverer.resolveDeclaredEntityType(callbackType).getRawClass());
    ......
}

after:

@Override
public <T> T callback(Class<? extends EntityCallback> callbackType, T entity, Object... args) {

    Assert.notNull(entity, "Entity must not be null");
    
    Class<T> entityType = (Class<T>) ClassUtils.getUserClass(entity.getClass());
    ......
}

[mp911de]

Thank you for your contribution. That's merged, polished, and backported now.