remove function slugify(filename_of_cashed_image);

revert wrong commit:
https://github.com/myopencart/ocStore/commit/bfdf3d575a6bd1dcc9f1a9e78ec76e07f295f5a7

description:
http://opencartforum.ru/topic/27002-процесс-работ-над-релизом-ocstore-15512/?p=220044