Update comments in dialog.scss for more clarity

Author: PooSham

src/material-experimental/mdc-dialog/dialog.scss

@@ -29,7 +29,8 @@ $mat-dialog-button-horizontal-margin: 8px !default;
   // aligns actions at the end of the container.
   justify-content: start;
 
-  // .align-center and .align-end are set by directive input "align"
+  // .mat-mdc-dialog-actions-align-{center|end} are set by directive input "align"
+  // [align='center'] and [align='right'] are kept for backwards compability
   &.mat-mdc-dialog-actions-align-center, &[align='center'] {
     justify-content: center;
   }

src/material/dialog/dialog.scss

@@ -56,7 +56,7 @@ $button-margin: 8px !default;
   // Pull the actions down to avoid their padding stacking with the dialog's padding.
   margin-bottom: -$padding;
 
-  // .align-center and .align-end are set by directive input "align"
+  // .mat-dialog-actions-align-{center|end} are set by directive input "align"
   // [align='center'] and [align='right'] are kept for backwards compability
   &.mat-dialog-actions-align-center, &[align='center'] {
     justify-content: center;