Remove Explicit core/drupal Dependency from same_page_preview library

Opened MR with this change.

@cosmicdreams Yes, I think the jQuery dependency needs to stay. Given the efforts to remove jQuery from core, there could possibly be a situation where it is removed from the core dependency that currently provides it, but we're still depending on jQuery in our code. Pretty unlikely, but possible. Also my understanding is that the cost of declaring a duplicate dependency is very low. It gets de-duped in the attachments array anyway.

RTBC then, merge when ready.