Remove any remaining references to old UI Events spec from PE

[patrickhlauke]

From the last PEWG meeting https://www.w3.org/2026/05/06-pointerevents-minutes.html#11a1

plh: for pointer events, do we still have dependency on UI events spec? if that spec disappears, would it affect PE?

plh: are we still referencing UI events normatively? yes we are...

plh: and there is still link to keyboard event

olli: that should go to editing WG conceptually

[plehegar]

@plehegar should investigate with moving keyboard events into the Web Editing working Group.

[plehegar]

timeline: making sure we know about the plan by TPAC