Remove entity_uri() support from views because it hasn't existed since 2012

Removing the code first to see if the test coverage still passes, I think it probably will.

No wait I'm wrong, or at least, it's not definitely dead/redundant.

EntityBase::toUrl() still does this:

    // Pass the entity data through as options, so that alter functions do not
    // need to look up this entity again.
    $uri
      ->setOption('entity_type', $this->getEntityTypeId())
      ->setOption('entity', $this);

I think this eventually gets passed down as undocumented keys in the $options array in OutboundPathProcessorInterface::processOutbound()
If that's the case, it might be valid after all, or... we might want to remove entity and entity_type from options in EntityBase::toUrl() instead.