message reaction list: Hide emails from user list.

Remove user emails from the user list in the message reactions
screen because in this context, the emails mostly feel like clutter.

As a side effect of this change, we no longer have to worry about
the server 'email_address_visibility' setting for this screen.

Fixes: zulip#4188

src/reactions/ReactionUserList.js

@@ -42,7 +42,6 @@ class ReactionUserList extends PureComponent<Props> {
               fullName={user.full_name}
               avatarUrl={user.avatar_url}
               email={user.email}
-              showEmail
               onPress={() => {
                 this.handlePress(user.user_id);
               }}