Removed php sniffer to test and fix upstream issue

Currently admin-eguide is not capable of building an image due to a dependency brought up by the dealerdirect/phpcodesniffer-composer-installer plugin.

From my understanding ,this plugin is not necessary for production websites and by removing it we are both cleaning up unnecessary dependencies on the live image, as well enabling admin-eguide to build images again (making the website go back to a normal state).

Since the full usage of the plugin is unknown to us, please discuss before merging