MDL-82214 admin: Settings should not change when in read only mode

Before this change if some settings were:

* read only
* visible on a settings page
* are set or have values selected

when the settings page was saved the setting would be set tobe empty,
because the hidden input remained on the page, while the other inputs
where not posted to Moodle.

admin/templates/setting_configcheckbox.mustache

@@ -38,6 +38,6 @@
     }
 }}
 <div class="form-checkbox defaultsnext">
-    <input type="hidden" name="{{name}}" value="{{no}}">
+    {{^readonly}}<input type="hidden" name="{{name}}" value="{{no}}">{{/readonly}}
     <input {{#readonly}}disabled{{/readonly}} type="checkbox" name="{{name}}" value="{{value}}" id="{{id}}" {{#checked}}checked{{/checked}}>
 </div>

admin/templates/setting_configmulticheckbox.mustache

@@ -35,7 +35,7 @@
     }
 }}
 <div class="form-multicheckbox">
-    <input type="hidden" name="{{name}}[xxxxx]" value="1">
+    {{^readonly}}<input type="hidden" name="{{name}}[xxxxx]" value="1">{{/readonly}}
     {{#hasoptions}}
         <ul>
             {{#options}}

admin/templates/setting_configmultiselect.mustache

@@ -40,7 +40,7 @@
     Setting configmultiselect.
 }}
 <div class="form-select">
-    <input type="hidden" name="{{name}}[xxxxx]" value="1">
+    {{^readonly}}<input type="hidden" name="{{name}}[xxxxx]" value="1">{{/readonly}}
     <select {{#readonly}}disabled{{/readonly}} id="{{id}}" name="{{name}}[]" size="{{size}}" class="form-control" multiple>
         {{#options}}
             <option value="{{value}}" {{#selected}}selected{{/selected}}>{{name}}</option>

admin/templates/setting_configmultiselect_optgroup.mustache

@@ -59,7 +59,7 @@
     Setting configmultiselect with optgroup support.
 }}
 <div class="form-select">
-    <input type="hidden" name="{{name}}[xxxxx]" value="1">
+    {{^readonly}}<input type="hidden" name="{{name}}[xxxxx]" value="1">{{/readonly}}
     <select {{#readonly}}disabled{{/readonly}} id="{{id}}" name="{{name}}[]" size="{{size}}" class="form-control" multiple>
     {{#options}}
         <option value="{{value}}" {{#selected}}selected{{/selected}}>{{name}}</option>