default streams: Fix overly aggressive typeahead.

When you select a typeahead, it shouldn't
immediately do the action for you; you should
have to hit enter first.  Even though 99% of
the time you're gonna confirm the typeahead,
it's jarring when you don't expect it.

You can still add a bunch of default streams
quickly, using only the keyboard, because
we have always had support for the enter
key saving.  (and tab and enter also works)

static/js/settings_streams.js

@@ -119,9 +119,6 @@ exports.build_page = function () {
         highlighter: function (item) {
             return typeahead_helper.render_typeahead_item({ primary: item });
         },
-        updater: function (stream_name) {
-            make_stream_default(stream_name);
-        },
     });
 
     $(".default-stream-form").on("click", "#do_submit_stream", function (e) {