Avoid "live edge" jargon in translations

In our source messages, we described two of them in terms of the "live
edge" of a video stream.  This is jargon that is generally not known
to translators, so we should avoid that and use a term that they are
more likely to understand.  These messages now refer to the "live
broadcast", which our translation service advised us would be clearer.

b/142728863

Change-Id: Ia1d4c9ff4d40a0a6bed445f95ec2841fd8cb33aa

ui/locales/source.json

@@ -41,11 +41,11 @@
   },
   "SKIP_TO_LIVE": {
     "message": "Skip ahead to live",
-    "description": "Label for a button used to skip ahead to the live edge of a live video stream."
+    "description": "Label for a button used to skip ahead to the live broadcast."
   },
   "LIVE": {
     "message": "Live",
-    "description": "Label to indicate that a video is already playing at the live edge of a live video stream."
+    "description": "Label to indicate that a video is already playing at the live broadcast."
   },
   "MORE_SETTINGS": {
     "message": "More settings",