Remove dead code written for PHP 5.2
diff --git a/system/libraries/Migration.php b/system/libraries/Migration.php
index 316c94a..3e2107e 100644
--- a/system/libraries/Migration.php
+++ b/system/libraries/Migration.php
@@ -288,10 +288,7 @@
 				$this->_error_string = sprintf($this->lang->line('migration_class_doesnt_exist'), $class);
 				return FALSE;
 			}
-			// method_exists() returns true for non-public methods,
-			// while is_callable() can't be used without instantiating.
-			// Only get_class_methods() satisfies both conditions.
-			elseif ( ! in_array($method, array_map('strtolower', get_class_methods($class))))
+			elseif ( ! is_callable(array($class, $method)))
 			{
 				$this->_error_string = sprintf($this->lang->line('migration_missing_'.$method.'_method'), $class);
 				return FALSE;