Add CSS rules for legacy dash deprecation warnings

lms/static/sass/course/instructor/_instructor.scss

@@ -2,6 +2,11 @@
   display: table;
   position: relative;
 
+  // deprecated content
+  .deprecated {
+    font-style: italic;
+  }
+
   .beta-button-wrapper {
     position: absolute;
     top: 2em;

lms/templates/courseware/legacy_instructor_dashboard.html

@@ -201,13 +201,17 @@ function goto( mode)
     </div>
     % endif
 
-    <p>
+    <p class="deprecated">
       ${_("To view the Gradebook (small courses only), please visit the 'Student Admin' section of the instructor dashboard.")}
     </p>
     <p>
     <input type="submit" name="action" value="Dump list of enrolled students" class="${'is-disabled' if disable_buttons else ''}">
     </p>
 
+    <p class="deprecated">
+      ${_("To perform grade downloads, please visit the 'Data Download' section of the instructor dashboard.")}
+    </p>
+
     <p class="is-deprecated">
       ${_("To download student grades, please visit the 'Data Download' section of the instructor dashboard.")}
     </p>
@@ -263,13 +267,13 @@ function goto( mode)
   %if settings.FEATURES.get('ENABLE_INSTRUCTOR_BACKGROUND_TASKS'):
     <H2>${_("Course-specific grade adjustment")}</h2>
 
-    <p>${_("To perform these actions, please visit the 'Student Admin' section of the instructor dashboard.")}</p>
+    <p class="deprecated">${_("To perform these actions, please visit the 'Student Admin' section of the instructor dashboard.")}</p>
 
   %endif
 
     <h2>${_("Student-specific grade inspection and adjustment")}</h2>
 
-    <p>${_("To perform these actions, please visit the 'Student Admin' section of the instructor dashboard.")}</p>
+    <p class="deprecated">${_("To perform these actions, please visit the 'Student Admin' section of the instructor dashboard.")}</p>
 
  %endif