webkitgtk24: mark as deprecated

webkitgtk24: mark as deprecated

It's affected by 40+ security bugs, and upstream will only care to fix
the latest stable branch, which is 2.12.x
Some effort was made with the 2.4.10 release to address some security
bugs but it's incomplete.

See:
https://blogs.gnome.org/mcatanzaro/2016/02/01/on-webkit-security-updates/
https://blogs.gnome.org/mcatanzaro/2016/02/19/webkitgtk-gets-security-updates/

Also:
http://webkitgtk.org/security/WSA-2016-0002.html
http://webkitgtk.org/security/WSA-2016-0001.html
http://webkitgtk.org/security/WSA-2015-0002.html

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>