Make safety numbers singular in webrtc call screen

Closes #6148
// FREEBIE

res/values/strings.xml

@@ -648,10 +648,8 @@
     <string name="SingleRecipientNotificationBuilder_new_message">New message</string>
 
     <!-- WebRtcCallScreen -->
-    <string name="WebRtcCallScreen_new_safety_numbers">The safety numbers for your conversation with %1$s have changed. This could either mean that someone is trying to intercept your communication, or that %2$s simply re-installed Signal.</string>
-    <string name="WebRtcCallScreen_you_may_wish_to_verify_this_contact">You may wish to verify
-        safety numbers for this contact.
-    </string>
+    <string name="WebRtcCallScreen_new_safety_numbers">The safety number for your conversation with %1$s has changed. This could either mean that someone is trying to intercept your communication, or that %2$s simply re-installed Signal.</string>
+    <string name="WebRtcCallScreen_you_may_wish_to_verify_this_contact">You may wish to verify your safety number with this contact.</string>
     <string name="WebRtcCallScreen_new_safety_numbers_title">New safety numbers</string>
 
     <!-- WebRtcCallControls -->