DONTBUILD because this is just whitespace cleanup.
Note: mccr8 mentioned in D160577 that this is MSCOM IDL and not XPIDL, for what
it's worth. In any case, there doesn't seem to be any functional significance
to the tab character that I'm removing here, since it's in a declaration
pattern that's repeated in this file, and only this one instance has stray tab
before the closing-paren.
Depends on D160577
Differential Revision: https://phabricator.services.mozilla.com/D160580
