8230290: [JVMCI] Remove unused API entry points

Remove VirtualObject.setIsAutoBox()

Reviewed-by: kvn

Author: Igor Veresov

src/jdk.internal.vm.ci/share/classes/jdk.vm.ci.code/src/jdk/vm/ci/code/VirtualObject.java

@@ -240,17 +240,6 @@ public boolean isAutoBox() {
         return isAutoBox;
     }
 
-    /**
-     * Sets the value of the box flag.
-     *
-     * @param isAutoBox a flag that tells the runtime that the object may be a boxed primitive and
-     *            that it possibly needs to be obtained for the box cache instead of creating a new
-     *            instance.
-     */
-    public void setIsAutoBox(boolean isAutoBox) {
-        this.isAutoBox = isAutoBox;
-    }
-
     /**
      * Overwrites the current set of values with a new one.
      *