Remove libjpeg-turbo native libs and plugin

[randomorder]

taking into account the results of our tests in #150, we want to remove the libjpeg-turbo native libraries build and install as well as the related geoserver plugin from the docker images.

Remove all references to the native lib build and install, from the dockerfile

• https://github.com/geosolutions-it/docker-geoserver/blob/master/Dockerfile#L145
• https://github.com/geosolutions-it/docker-geoserver/blob/master/Dockerfile#L97
• https://github.com/geosolutions-it/docker-geoserver/blob/master/Dockerfile#L145

As well as from the docker build hooks

[randomorder]

thanks @mo3rfan