Prevent Gtk from being installed in the Docker container

[probonopd]

Prevent Gtk from being installed in the Docker container.
What is pulling it in?

[probonopd]

Docker and CMake... cost me way too much time today. And I still don't know why Gtk is ending up in the Docker container.

[TheAssassin]

What Docker container do you mean? You're not providing nearly enough information...

[TheAssassin]

Could you please stop experimenting on main? This is really bad style.

[probonopd]

What Docker container do you mean? You're not providing nearly enough information...

The Docker container that builds the AppImageUpdate AppImages.

Could you please stop experimenting on main? This is really bad style.

Thing is, with each commit I thought "this is it". Didn't imagine it to be so hard. Will work on a branch next time.

[TheAssassin]

As mentioned in #150 (comment), this is simply the wrong question to ask. All these commits are really, really, really bad hacks. The Gtk+ stuff is pulled in as dependencies of the packages.

Closing here therefore in favor of #150. I'll push a single-commit revert for all these previous commits, and will fix the issue in linuxdeploy-plugin-qt.