Remove CSS option no longer supported in Chart.js

From the migration notes for version 3 noting the
removal of Chart.platform:

    It only contained disableCSSInjection. CSS is never injected in v3.

https://www.chartjs.org/docs/master/migration/v3-migration.html

share/static/js/util.js

@@ -713,8 +713,6 @@ jQuery(function() {
         this.$element.val('').change().focus();
     };
 
-    Chart.platform.disableCSSInjection = true;
-
     // Make actions dropdown scrollable in case screen is too short
     jQuery(window).resize(function() {
         jQuery('#li-page-actions > ul').css('max-height', jQuery(window).height() - jQuery('#rt-header-container').height());