PHP 5 is dead, long live PHP 7

This commit removes support for PHP 5 by getting rid of all of our Zend
compatibility layer methods, as well as any call checking against
PHP_MAJOR_VERSION or ZEND_MODULE_API_NO.

Unit tests are all passing for Redis, RedisCluster, and RedisArray but
this should still be considered a work in progress until more testing
can be done.

Addresses issue #1448

redis_session.h

@@ -11,10 +11,8 @@ PS_DESTROY_FUNC(redis);
 PS_GC_FUNC(redis);
 PS_CREATE_SID_FUNC(redis);
 
-#if (PHP_MAJOR_VERSION >= 7)
 PS_VALIDATE_SID_FUNC(redis);
 PS_UPDATE_TIMESTAMP_FUNC(redis);
-#endif
 
 PS_OPEN_FUNC(rediscluster);
 PS_CLOSE_FUNC(rediscluster);