Clean up unused Sliceable.copy()

Sliceable.isCopyableSlice() is not set to true for any controller, so this function is not used.

Usage is removed in Change: I81474aed994678c42d73cc59e169573880de1378

Bug: 227722942
Test: robotest & manual
Change-Id: I86e23aa8ad43f60b5017ff0a278e20e3f727706c

src/com/android/settings/slices/Sliceable.java

@@ -88,20 +88,6 @@ public interface Sliceable {
         return false;
     }
 
-    /**
-     * Copy the key slice information to the clipboard.
-     * It is highly recommended to show the toast to notify users when implemented this function.
-     */
-    default void copy() {
-    }
-
-    /**
-     * Whether or not it's a copyable slice.
-     */
-    default boolean isCopyableSlice() {
-        return false;
-    }
-
     /**
      * Whether or not summary comes from something dynamic (ie, not hardcoded in xml)
      */