d/rules: remove web ui pre-built files (Closes: 990340)

This just remove the glances/outputs/static/public/ directory.

Building the Web UI from sources requires npm packages not available in Debian, like angular, this is short-term solution fixing the RC bug.

To build the package and import the dfsg repacked orig tarball, you can do these commands (this is what I used to check the generated package):

uscan --download-current-version
gbp import-orig --pristine-tar --no-interactive  ../glances_3.1.5+dfsg.orig.tar.gz
gbp dch -Ra --commit