Replace .parent() for .closest in buddypress.js

[hnla]

In the same manner of previous tickets on this aspect another .parent().parent().parent() has caused issues with adjusted markup causing activity unfav in activity favourit view jumping it's slideUp() to the wrong parent node and hiding all the activity items rather than the activity-item in question.

Patch replaces .parent() with .closest('activity-item')

[hnla]

change .parent() to .closest() for activity unfav

[boonebgorges]

In 8138:

Use closest() instead of parent() to hide unfavorited activity item

Ancestor-crawling makes for inflexible javascript, which makes for sad developers.

Fixes #5467

Props hnla