Use mainstream theme solution for gnome-terminal, drop patch

[Egmont Koblinger]

Ubuntu adds a patch called "0001-Add-style-classes-and-CSS-names-to-some-of-our-widge.patch" to gnome-terminal, and in turn Ambiance and Radiance themes' apps/gnome-terminal.css relies on this to get the desired look for the notebook widget.

Beginning with gnome-terminal 3.20.3 / 3.22.1 this should no longer be necessary. It's just an additional burden to carry this patch, plus an unnecessary complication for those who wish to manually compile gnome-terminal for whatever reason.

gnome-terminal.css should ideally be modified to use the CSS names provided by mainstream gnome-terminal, and once done, the gnome-terminal patch can be dropped.

Upstream references:
https://bugzilla.gnome.org/show_bug.cgi?id=765590
https://bugzilla.gnome.org/show_bug.cgi?id=772134#c6
https://bugzilla.gnome.org/show_bug.cgi?id=788044

[Daniel van Vugt (vanvugt)]

Thank you for reporting this bug to Ubuntu.

Ubuntu 17.10 (artful) reached end-of-life on July 19, 2018.

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