authPrompt: Remove colons from questions

Unfortunately, the question that is displayed comes directly
from PAM. It usually is just "Password:", which comes from
pam-unix, but other questions can be set, usually with the
colons, since they are crafted with a CLI workflow in mind.

Manually drop the colons from questions asked by PAM. This
is also done by the PolKit agent, which shows how the stack
is fragile, but it's what we have for now.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/922

js/gdm/authPrompt.js

@@ -209,7 +209,8 @@ var AuthPrompt = GObject.registerClass({
         }
 
         this._updateEntry(secret);
-        this.setQuestion(question);
+        // HACK: the question comes directly from PAM
+        this.setQuestion(question.replace(/: *$/, '…').trim());
 
         this.updateSensitivity(true);
         this.emit('prompted');