Remove link node inspector from insert menu

This inspector isn't designed for insertion mode yet; attempting to use
it in insertion mode causes nasty JS errors.

Bonus:
* Make its tool title "Simple link" rather than "Link", for when
  we do reintroduce it.
* Make double-clicking / pressing enter while selecting a link node
  open the link node inspector rather than the link annotation inspector.
* Make link nodes render with MW's external link arrow icon
* Move the link node inspector's messages to the right RL module

Bug: 66047
Change-Id: Ib94da7ed3a2a88297dbdd1529f20cd8dab7c8421
Merge "Remove link node inspector from insert menu"