actor: Plug a leak in the implicit transition removal

We need to release the temporary reference we acquired in order for the
signal emission to work.

https://bugzilla.gnome.org/show_bug.cgi?id=734761

Signed-off-by: Emmanuele Bassi <ebassi@gnome.org>
build: Remove experimental notice for wayland/evdev

Both backends are built via CI and used by GNOME, so they should not be
considered experimental any more.
evdev: Fix compiler warning
docs: Add missing symbols to the section file
Release Clutter 1.19.8
Post-release version bump to 1.19.9
Forgot to commit the NEWS file prior to release