Fix PageTriage JS dialog parameter

It was using .attr( 'value' ) to retrieve deletion details instead of val().
Also wrap a naked wgFoo variable access with mw.config.get().

Fixes T84996
Fixes T85184

Bug: T84996
Bug: T85184
Change-Id: I707930ae3f61615d79fbd3283269d6a3c1429525
(cherry picked from commit 0d5e57d639545dfc4c8e47c0a615655266513708)