Bug#996690: clutter-1.0: upstream project discontinued, should be removed

[Simon McVittie]

Control: retitle -1 clutter-1.0: upstream project discontinued, should be removed
Control: forcemerge -1 1018109

Clutter has now been moved to https://gitlab.gnome.org/Archive/clutter and
it's in the process of being archived. After that has happened, no new
bugs can be reported, no new commits can be pushed, and no new releases
will be made.

    smcv