Port away from I18N_NOOP2 and KLocalizedString::insertQtDomain

Summary:

• Remove duplication of the untranslated (but marked for translation)

string. "Home" is "Home" even after marking for translation, no need to pass
it twice. Pass the context (so I18NC_NOOP can be used) and discard it.

• Messages.sh covers all of kio, there's no Qt linguist file involved

here.

Test Plan:
Builds, and the file places widget looks ok in Dolphin,
both in English and in French (LC_ALL=fr_FR dolphin).

Reviewers: aacid, ilic

Reviewed By: aacid

Subscribers: kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D24970