feat: Drop the unused edit view template.

And update the studio-view function to raise a NotImplementedError since
we now rely on the authoring environment to provide the edit view of
this block.

Unfortunately, a copy of the template lives in the lms and relies on the
the underlying JS and CSS to render a tiny-mce editor in the instructor
dashboard. This means we can't remove the CSS and JS until we've dropped
the usage of it in the instructor dash.  The good news is, that the work
to replace the instructor dash is in progress so those assets should get
cleaned up soon.

The places where the JS and CSS is still being used are:

* lms/templates/instructor/instructor_dashboard_2/instructor_dashboard_2.html
* lms/djangoapps/instructor/views/instructor_dashboard.py

cms/templates/widgets/html-edit.html

@@ -1,13 +0,0 @@
-<%! from django.utils.translation import gettext as _ %>
-
-<div class="wrapper-comp-editor" id="editor-tab" data-base-asset-url="${base_asset_url}" data-editor="${editor}">
-    <section class="html-editor editor">
-      <div class="row">
-          % if editor == 'visual':
-            <textarea class="tiny-mce">${data | h}</textarea>
-          % endif
-          <textarea name="" class="edit-box">${data | h}</textarea>
-      </div>
-    </section>
-</div>
-<%include file="metadata-edit.html" />

xmodule/html_block.py

@@ -142,13 +142,7 @@ class HtmlBlockMixin(  # lint-amnesty, pylint: disable=abstract-method
         """
         Return the studio view.
         """
-        fragment = Fragment(
-            self.runtime.service(self, 'mako').render_cms_template(self.mako_template, self.get_context())
-        )
-        add_css_to_fragment(fragment, 'HtmlBlockEditor.css')
-        add_webpack_js_to_fragment(fragment, 'HtmlBlockEditor')
-        shim_xmodule_js(fragment, 'HTMLEditingDescriptor')
-        return fragment
+        raise NotImplementedError
 
     @classmethod
     def get_customizable_fields(cls) -> dict[str, str | None]: