The column mentionedRemoteUsers on the note table in the database is
firstly in the wrong type since it contains JSON data but is typed as
text. Secondly it seems redundant, since that data can be acquired by
using the note.mentions column to fetch the respective data instead.
Removed the misc/get-note-html module which was only used in one place.
Instead of it, the general MFM to HTML functionality has been improved to
take care of the use cases of that module as well.