Removed DateTimeImmutable::createFromInterface() from stubs

While there is value in declaring `DateTimeImmutable::createFromInterface()` as mutation-free in
a stub, this method was introduced in PHP 8.0, so we cannot really declare it in a stub.

For now, we drop it, as the value of its stub declaration is much lower than the problems it
introduces through its conditional existence.

stubs/CoreImmutableClasses.phpstub

@@ -100,12 +100,6 @@ class DateTimeImmutable implements DateTimeInterface
      * @return static
      */
     public static function createFromMutable(DateTime $object) {}
-
-    /**
-     * @psalm-mutation-free
-     * @return self
-     */
-    public static function createFromInterface(DateTimeInterface $object) {}
 }
 
 /**