Update return type of getInnerIterator which is always returning an iterator

[drupol]

When an iterator implements OuterIterator interface, it has the getInnerIterator method, which is always returning an iterator.

This PR:

• Update CallMap.php and CallMap_historical.php to reflect this.

[weirdan]

Note: even though docs say it returns ?Iterator the stated intention of OuterIterator is to implement it in iterator wrapper classes, so the null part in that union doesn't really make sense.

[weirdan]

Thanks!

[drupol]

Thanks for merging !