refactor(expansion): avoid unnecessary spacing check

The check where `expanded` equals to `false`, and where the value of
the `_getExpandedState` method is compared to `default` will always
evaluate to `false`. This is because the method return value does not
have any overlap with `default`. Hence the check is unnecessary.

This seems to be a leftover from f9bd5d4.

Author: devversion

src/material/expansion/expansion-panel.ts

@@ -185,7 +185,7 @@ export class MatExpansionPanel extends CdkAccordionItem implements AfterContentI
       // We don't need to subscribe to the `stateChanges` of the parent accordion because each time
       // the [displayMode] input changes, the change detection will also cover the host bindings
       // of this expansion panel.
-      return (this.expanded ? this.accordion.displayMode : this._getExpandedState()) === 'default';
+      return this.expanded && this.accordion.displayMode === 'default';
     }
     return false;
   }