MDL-67968 question: do not display sr-only legends

.accesshide was removed because:
 1. It was only kept in case it's still used somewhere, in a custom form
 field for instance.
 2. It was broken since 3.5 where we integrated
 bmbrands/moodle@ab65b87...MDL-62419-master
 So it's been ages that the reason mentioned on point 1 was not being
 satisfied

theme/boost/scss/moodle/question.scss

@@ -221,12 +221,7 @@
 
 body.path-question-type {
     /* Hacks to display the labels within a form group. */
-    .fitem_fgroup .accesshide {
-        font: inherit;
-        position: static;
-        padding-right: .3em;
-    }
-    .form-group .sr-only {
+    .form-group .sr-only:not(legend) {
         position: static;
         width: auto;
         height: auto;

theme/boost/style/moodle.css

@@ -14917,11 +14917,7 @@ a.ygtvspacer:hover {
 
 body.path-question-type {
   /* Hacks to display the labels within a form group. */ }
-  body.path-question-type .fitem_fgroup .accesshide {
-    font: inherit;
-    position: static;
-    padding-right: .3em; }
-  body.path-question-type .form-group .sr-only {
+  body.path-question-type .form-group .sr-only:not(legend) {
     position: static;
     width: auto;
     height: auto;

theme/classic/style/moodle.css

@@ -15135,11 +15135,7 @@ a.ygtvspacer:hover {
 
 body.path-question-type {
   /* Hacks to display the labels within a form group. */ }
-  body.path-question-type .fitem_fgroup .accesshide {
-    font: inherit;
-    position: static;
-    padding-right: .3em; }
-  body.path-question-type .form-group .sr-only {
+  body.path-question-type .form-group .sr-only:not(legend) {
     position: static;
     width: auto;
     height: auto;