d/control: Don't pull in gnome-themes-extra

Simon McVittierequested to merge
wip/bug1077864 into debian/latest

For users of legacy GTK 2 apps, GTK 2 itself now Recommends this.

Closes: #1077864

Blocked by updates to gtk+2.0 and gnome-themes-extra (test-build currently in progress) but I wanted to open the merge request even though it can't land right now.

/cc @jbicha

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