fix(material-experimental): remove mixin which no longer exists from mdc

Author: josephperrott

src/material-experimental/mdc-core/option/optgroup.scss

@@ -3,7 +3,6 @@
 @import '@material/list/variables.import';
 
 .mat-mdc-optgroup-label {
-  @include mdc-list-deprecated-item-base_;
   @include mdc-list-deprecated-list-item-padding-variant(
     $mdc-list-deprecated-textual-variant-config, $query: mdc-helpers.$mat-base-styles-query);
   @include mdc-list-deprecated-list-item-height-variant(

src/material-experimental/mdc-core/option/option.scss

@@ -7,9 +7,6 @@
 @import '@material/list/variables.import';
 
 .mat-mdc-option {
-  // Note that we include this private mixin, because the public
-  // one adds a bunch of styles that we aren't using for the menu.
-  @include mdc-list-deprecated-item-base_;
   @include mdc-list-deprecated-list-item-padding-variant(
     $mdc-list-deprecated-textual-variant-config, $query: mdc-helpers.$mat-base-styles-query);
   @include mdc-list-deprecated-item-disabled-text-opacity(

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

@@ -41,9 +41,6 @@ mat-menu {
     $property-name: height,
   );
 
-  // Note that we include this private mixin, because the public
-  // one adds a bunch of styles that we aren't using for the menu.
-  @include mdc-list-deprecated-item-base_;
   @include mdc-list-deprecated-list-item-padding-variant(
     $mdc-list-deprecated-textual-variant-config, $query: mdc-helpers.$mat-base-styles-query);