Leaves behind tables

I deleted because it was unable to download optimised images.

(1) After deactivation, plugin leaves the following tables:

* wp_shortpixel_folders
* wp_shortpixel_meta
* wp_shortpixel_postmeta
* wp_shortpixel_queue

(2) After deletion, the following tables remain:

* wp_shortpixel_folders
* wp_shortpixel_meta
* wp_shortpixel_postmeta

(3) After deletion, the following folder remains:

* /uploads/ShortpixelBackups