Disable more useless GNOME session processes on Jessie

E.g. we’re currently running /usr/lib/evolution/evolution-source-registry, /usr/lib/gnome-shell/gnome-shell-calendar-server, and /usr/lib/telepathy/mission-control-5. Probably not all of those are useful in Tails. Getting rid of some of them would help avoid Tails/Jessie require too much RAM.

Related issues

Related to #7986 (closed)

Original created by @intrigeri on 9037 (Redmine)

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