Cleanup skip/teardown workaround #cosmetic

this.skip() skips teardown; the code that would have run is
$('#mock').empty(), whereas el.remove() is specific to how this test
currently works and is more brittle, do the general thing instead.
diff --git a/test/unit/saneKeyboardEvents.test.js b/test/unit/saneKeyboardEvents.test.js
index 41284ea..4b14149 100644
--- a/test/unit/saneKeyboardEvents.test.js
+++ b/test/unit/saneKeyboardEvents.test.js
@@ -156,7 +156,7 @@
           'clicked on something in the Developer Tools or on the page itself. ' +
           'Click the page, or close the Developer Tools, and Refresh.'
         );
-        el.remove(); // LOL next line skips teardown https://git.io/vaUWq
+        $('#mock').empty(); // LOL next line skips teardown https://git.io/vaUWq
         this.skip();
       }