Update terminology once whatwg/html#8463 is fixed

[sbingler]

#2480 updated 6265bis with new HTML terminology, but "target browsing context" wasn't yet changed. whatwg/html#8463 is tracking that work and once it is fixed then 6265bis can use the updated term.

See
#2480 (comment)
#2480 (comment)

This is low priority work and may be deferred if needed.