Delete some dom walker code (#6304)

**Problem:**
I started from deleting the reconstructedMetadata parameter from the
editorDispatchActionRunner function (mentioned here:
#6240 (comment)
), and ended up deleting a whole bunch of old dom-walker code.

Probably there is still some unnecessary code left, but I believe it was
still useful to wipe some of the not running and unnecessary code.

**Manual Tests:**
I hereby swear that:

- [x] I opened a hydrogen project and it loaded
- [x] I could navigate to various routes in Preview mode