MSC4210: Remove legacy mentions (#4210)
* Remove legacy mentions
Signed-off-by: Tulir Asokan <tulir@maunium.net>
* Add another potential issue
Signed-off-by: Tulir Asokan <tulir@maunium.net>
* Add new room version to alternatives
Signed-off-by: Tulir Asokan <tulir@maunium.net>
* Specify that including `m.mentions` in all events is still necessary
Signed-off-by: Tulir Asokan <tulir@maunium.net>
* Add links to current spec
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Signed-off-by: Tulir Asokan <tulir@maunium.net>
