Move print-editor to demos

It is too demo-esque for languishing in tests/.

demos/meson.build

@@ -3,3 +3,4 @@ subdir('gtk-demo')
 subdir('icon-browser')
 subdir('node-editor')
 subdir('widget-factory')
+subdir('print-editor')

demos/print-editor/meson.build

@@ -0,0 +1,6 @@
+executable('print-editor',
+           ['print-editor.c'],
+           c_args: common_cflags,
+           dependencies: libgtk_dep,
+           include_directories: confinc,
+           gui_app: true)

tests/meson.build

@@ -10,7 +10,6 @@ gtk_tests = [
   ['scrolling-performance', ['frame-stats.c', 'variable.c']],
   ['blur-performance', ['../gsk/gskcairoblur.c']],
   ['simple'],
-  ['print-editor'],
   ['video-timer', ['variable.c']],
   ['testaccel'],
   ['testadjustsize'],