snap: Upgrade from gnome-3-28 extension to gnome-3-34

Using gnome-3-34 gives us a newer stack in general
and also provides us with a sdk build-snap, so we don't need
to specify as many build-packages and stage-packages.

This makes the snap slimmer and delegates the responsibility
for security updates to the gnome platform snap for even more
packages.

pkg/snap/snap/snapcraft.yaml

@@ -23,13 +23,13 @@ apps:
   solvespace:
     command: usr/bin/solvespace
     desktop: solvespace.desktop
-    extensions: [gnome-3-28]
+    extensions: [gnome-3-34]
     plugs: [opengl, unity7, home, removable-media, gsettings, network]
     environment:
       __EGL_VENDOR_LIBRARY_DIRS: $SNAP/gnome-platform/usr/share/glvnd/egl_vendor.d:$SNAP/usr/share/glvnd/egl_vendor.d
   cli:
     command: usr/bin/solvespace-cli
-    extensions: [gnome-3-28]
+    extensions: [gnome-3-34]
     plugs: [home, removable-media, network]
 
 parts:
@@ -54,32 +54,25 @@ parts:
     build-packages:
       - zlib1g-dev
       - libpng-dev
-      - libcairo2-dev
       - libfreetype6-dev
       - libjson-c-dev
-      - libfontconfig1-dev
-      - libgtkmm-3.0-dev
-      - libpangomm-1.4-dev
       - libgl-dev
-      - libglu-dev
+      - libsigc++-2.0-dev
       - libspnav-dev
       - git
+      - g++
     stage-packages:
       - libspnav0
-      - libatkmm-1.6-1v5
-      - libcairomm-1.0-1v5
-      - libgtkmm-3.0-1v5
-      - libglibmm-2.4-1v5
-      - libpangomm-1.4-1v5
       - libsigc++-2.0-0v5
+
   cleanup:
     after: [solvespace]
     plugin: nil
-    build-snaps: [core18, gnome-3-28-1804]
+    build-snaps: [core18, gnome-3-34-1804]
     override-prime: |
       # Remove all files from snap that are already included in the base snap or in
       # any connected content snaps
       set -eux
-      for snap in "core18" "gnome-3-28-1804"; do  # List all content-snaps and base snaps you're using here
+      for snap in "core18" "gnome-3-34-1804"; do  # List all content-snaps and base snaps you're using here
         cd "/snap/$snap/current" && find . -type f,l -exec rm -f "$SNAPCRAFT_PRIME/{}" \;
       done