msglist [nfc]: Remove unnecessary fontFamily argument.

We supplied the font 'Source Sans 3' to `TextTheme.bodyMedium` in
`lib/widgets/text.dart`. When rendered, `Material` applies this font via
`AnimatedDefaultTextStyle` by default, so there is no need to override
`fontFamily` explicitly.

See:

  zulip#900 (comment)

Signed-off-by: Zixuan James Li <[email protected]>

Author: PIG208

lib/widgets/message_list.dart

@@ -1231,7 +1231,6 @@ class MessageWithPossibleSender extends StatelessWidget {
                   Flexible(
                     child: Text(message.senderFullName, // TODO get from user data
                       style: TextStyle(
-                        fontFamily: 'Source Sans 3',
                         fontSize: 18,
                         height: (22 / 18),
                         color: messageListTheme.senderName,
@@ -1250,7 +1249,6 @@ class MessageWithPossibleSender extends StatelessWidget {
           Text(time,
             style: TextStyle(
               color: messageListTheme.messageTimestamp,
-              fontFamily: 'Source Sans 3',
               fontSize: 16,
               height: (18 / 16),
               fontFeatures: const [FontFeature.enable('c2sc'), FontFeature.enable('smcp')],