Removing MooTools dependencies from libraries folder

Under GSoC MooTools to jQuery project, this PR removes the MooTools dependencies in several functions of the libraries/cms/form/field/media.php file. 
Note: MooTools dependencies are not removed from the functions that are related to media libraries loading since they are removed with the respective library (e.g switcher.js) MooTools dependency removal PR.

Feature Request Item:
http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32029&start=550