[5.7] Remove duplicate code

[staudenmeir]

We don't need HasOneOrMany::update(), Builder::update() already adds the UPDATED_AT timestamp.

The tests expect the update() method in the HasOneOrMany class, so we have to remove them.

[GrahamCampbell]

We should probably keep the tests though. Duplicate testing is not necessarily a bad thing.

[staudenmeir]

@GrahamCampbell I don't really see the benefit. We would have to adjust them and then they would just test Builder::update() (which we already have tests for).

[dkulyk]

@staudenmeir You also can delete updateTimestamps from Model::performUpdate