remove ArrayTheoryISE

[MichaelRawson]

See #157. To quote the documentation in the header file:

 * The "extensionality resolution project" initially started out to improve
 * Vampire's reasoning in the theory of arrays. A first attempt was to add some
 * simple rewrite rules. However, the code here is not used at the moment.
 *
 * Adding this rewrite rules might be useful, but then the code has to be
 * revised. For example, applying rewrite rules exhaustively is implemented very
 * inefficiently.

...but it's been a decade since then. I don't think it's going to happen and theory reasoning has changed in that time.