Remove option for ‘disabled’ textbox

I think this was used for the invite page at one point, but isn’t now.

Generally at GDS we don’t do disabled form controls, they don’t tell you
_why_ they’re disabled.

app/templates/components/textbox.html

@@ -7,7 +7,6 @@
   help_link_text=None,
   width='2-3',
   suffix=None,
-  disabled=False,
   safe_error_message=False,
   rows=8
 ) %}
@@ -25,20 +24,11 @@
         </span>
       {% endif %}
     </label>
-      {% if disabled %}
-        <p>{{ field(**{
-          'class': 'form-control form-control-{} textbox-highlight-textbox'.format(width) if highlight_tags else 'form-control form-control-{} {}'.format(width, 'textbox-right-aligned' if suffix else ''),
-          'data-module': 'highlight-tags' if highlight_tags else '',
-          'disabled': 'disabled'
-        }) }}
-      </p>
-      {% else %}
-        {{ field(**{
-          'class': 'form-control form-control-{} textbox-highlight-textbox'.format(width) if highlight_tags else 'form-control form-control-{} {}'.format(width, 'textbox-right-aligned' if suffix else ''),
-          'data-module': 'highlight-tags' if highlight_tags else '',
-          'rows': rows|string
-        }) }}
-      {% endif %}
+    {{ field(**{
+      'class': 'form-control form-control-{} textbox-highlight-textbox'.format(width) if highlight_tags else 'form-control form-control-{} {}'.format(width, 'textbox-right-aligned' if suffix else ''),
+      'data-module': 'highlight-tags' if highlight_tags else '',
+      'rows': rows|string
+    }) }}
     {% if suffix %}
       <span>{{ suffix }}</span>
     {% endif %}