Move heading classes back to Reboot to prevent a dependency

scss/content/_reboot.scss

@@ -96,32 +96,38 @@ hr {
   color: var(--#{$prefix}heading-color);
 }
 
-h1 {
+h1,
+.h1 {
   @extend %heading;
   @include font-size($h1-font-size);
 }
 
-h2 {
+h2,
+.h2 {
   @extend %heading;
   @include font-size($h2-font-size);
 }
 
-h3 {
+h3,
+.h3 {
   @extend %heading;
   @include font-size($h3-font-size);
 }
 
-h4 {
+h4,
+.h4 {
   @extend %heading;
   @include font-size($h4-font-size);
 }
 
-h5 {
+h5,
+.h5 {
   @extend %heading;
   @include font-size($h5-font-size);
 }
 
-h6 {
+h6,
+.h6 {
   @extend %heading;
   @include font-size($h6-font-size);
 }

scss/content/_type.scss

@@ -3,35 +3,6 @@
 @use "../mixins/lists" as *;
 @use "../vendor/rfs" as *;
 
-//
-// Headings
-//
-// mdo-do: remove extend
-// .h1 {
-//   @extend h1;
-// }
-
-// .h2 {
-//   @extend h2;
-// }
-
-// .h3 {
-//   @extend h3;
-// }
-
-// .h4 {
-//   @extend h4;
-// }
-
-// .h5 {
-//   @extend h5;
-// }
-
-// .h6 {
-//   @extend h6;
-// }
-
-
 .lead {
   @include font-size($lead-font-size);
   font-weight: $lead-font-weight;