connection-editor: don't defer creation of vpn connection to idle

Now that GtkApplication makes good decisions about when to quit (when no
windows are present), the magic that deferred creation of vpn type
selector is useless. Worse even, it makes GtkApplication believe that
we're done and shuts it down before an editor window is added to it.

#9

Reported-by: Jan Tojnar
5 jobs for lr/vpn-add-idle in 16 minutes and 52 seconds (queued for 7 seconds)
latest
Status Job ID Name Coverage
  Build
passed #62852
fedora28_dist

00:07:39

 
  Test
passed #62856
fedora_autotools_full

00:09:10

passed #62855
fedora_autotools_minimal

00:07:26

passed #62854
fedora_meson_full

00:05:57

passed #62853
fedora_meson_minimal

00:03:57