Revert "Calendar: Remove leading zeros for 24h time format"

Leading zeros are common in the 24h format, and indeed used in the
wallclock in the top bar. Convention and consistency within the
same clock format trumps inconsistency between different time formats,
so reverting commit 316f825b2a.

https://bugzilla.gnome.org/show_bug.cgi?id=658675

js/ui/calendar.js

@@ -74,7 +74,7 @@ function _formatEventTime(event, clockFormat, periodBegin, periodEnd) {
         case '24h':
             /* Translators: Shown in calendar event list, if 24h format,
                \u2236 is a ratio character, similar to : */
-            ret = date.toLocaleFormat(C_("event list time", "%k\u2236%M"));
+            ret = date.toLocaleFormat(C_("event list time", "%H\u2236%M"));
             break;
 
         default: