Fix the binding of the checked and disabled properties of cr-checkbox.

Boolean binding is strange and in this case, we didn't actually want question marks in the bindings for the paper-checkbox's attributes. This makes everything work properly.

R=michaelpg
BUG=

Review URL: https://codereview.chromium.org/948283004

Cr-Commit-Position: refs/heads/master@{#318132}

ui/webui/resources/cr_elements/cr_checkbox/cr_checkbox.html

@@ -8,7 +8,7 @@
     <link rel="stylesheet" href="cr_checkbox.css">
     <cr-events id="events"></cr-events>
     <paper-checkbox id="checkbox"
-        checked?="{{checked}}" disabled?="{{disabled}}" label="{{label}}">
+        checked="{{checked}}" disabled="{{disabled}}" label="{{label}}">
     </paper-checkbox>
   </template>
   <script src="cr_checkbox.js"></script>

ui/webui/resources/cr_elements/cr_toggle_button/cr_toggle_button.html

@@ -8,7 +8,7 @@
     <link rel="stylesheet" href="cr_toggle_button.css">
     <cr-events id="events"></cr-events>
     <paper-toggle-button id="button"
-        checked?="{{ checked }}" disabled?="{{ disabled }}">
+        checked="{{checked}}" disabled="{{disabled}}">
     </paper-toggle-button>
   </template>
   <script src="cr_toggle_button.js"></script>