Fix JSInput test fixture

Clean up fixtures automatically between tests
- Nesting test fixture markup within a DIV allows Jasmine to
  automatically restore the fixture to a clean state between each test
  run.

Fix id attribute collision typo
- This looks like a copy/pasta gone wrong; the two test INPUT elements
  were both declared with the same id, `input_1`.

Remove trailing whitespace

common/static/js/capa/fixtures/jsinput.html

+<div>
 <section
   id="inputtype_1"
   data="getGrade"
@@ -45,6 +46,8 @@
       width="500"
       src="https://studio.edx.org/c4x/edX/DemoX/asset/webGLDemo.html">
     </iframe>
-    <input type="hidden" name="input_2" id="input_1" waitfor value="{&quot;answer&quot;:&quot;{\&quot;cylinder\&quot;:true,\&quot;cube\&quot;:true}&quot;,&quot;state&quot;:&quot;{\&quot;selectedObjects\&quot;:{\&quot;cylinder\&quot;:true,\&quot;cube\&quot;:true}}&quot;}">
+    <input type="hidden" name="input_2" id="input_2" waitfor value="{&quot;answer&quot;:&quot;{\&quot;cylinder\&quot;:true,\&quot;cube\&quot;:true}&quot;,&quot;state&quot;:&quot;{\&quot;selectedObjects\&quot;:{\&quot;cylinder\&quot;:true,\&quot;cube\&quot;:true}}&quot;}">
   </div>
 </section>
+</div>
+