Unify 32-bit/64-bit str_split tests

The 32-bit tests work on both 32-bit and 64-bit. I dropped the
64-bit variants as they only test one additional case that I don't
think adds particular value.

Author: nikic

ext/standard/tests/strings/str_split_variation6.phpt

@@ -1,9 +1,5 @@
 --TEST--
 Test str_split() function : usage variations - different integer values for 'split_length' argument
---SKIPIF--
-<?php
-if (PHP_INT_SIZE != 4) die("skip this test is for 32bit platform only");
-?>
 --FILE--
 <?php
 /*

ext/standard/tests/strings/str_split_variation6_64bit.phpt

@@ -1,9 +1,5 @@
 --TEST--
 Test str_split() function : usage variations - different integer values for 'split_length' with heredoc 'str'
---SKIPIF--
-<?php
-if (PHP_INT_SIZE != 4) die("skip this test is for 32bit platform only");
-?>
 --FILE--
 <?php
 /*