Fixed issue briannesbitt#883: reverted pull-request briannesbitt#548 …

…about issue briannesbitt#88

The realisation of initial issue briannesbitt#88 is wrong. The problem does not relies to `local` / `not local` timezone. Php handles date changes similar for both cases. So in fact changes was made 'fixes' non-local dates but local dates works same as before.
And it 'fixes' the problem and not actually fixes it because in fact the PHP handling of DST changing in non-UTC dates is quite right. If developer don't want to adjusting timestamp to DST change he should use UTC timezone.

Next commits reverted by hand because conflicts in automatic revert.

* Commit 2cc6988  Fix CS	07.12.2015 13:04	Lucas Michot
* Commit 5394301  Fix issue 88	07.12.2015 12:55	Lucas Michot

src/Carbon/Carbon.php

@@ -3317,27 +3317,6 @@ public function isBirthday(self $dt = null)
         return $this->isSameAs('md', $dt);
     }
 
-    /**
-     * Consider the timezone when modifying the instance.
-     *
-     * @param string $modify
-     *
-     * @return static
-     */
-    public function modify($modify)
-    {
-        if ($this->local) {
-            return parent::modify($modify);
-        }
-
-        $timezone = $this->getTimezone();
-        $this->setTimezone('UTC');
-        $instance = parent::modify($modify);
-        $this->setTimezone($timezone);
-
-        return $instance;
-    }
-
     /**
      * Return a serialized string of the instance.
      *