Remove vestigial sentence

Based on my reading of this section in the latest policy email...

12.7 Upstream release notes, when available, should be installed as /usr/share/doc/package/NEWS.gz. Upstream changelogs may be made available as /usr/share/doc/package/changelog.gz.

This is a relaxation of older Policy which said that the upstream changelog should be made accessible at this path. Now it is up to maintainer discretion whether it is useful to install it.

The practice of installing the upstream release notes as /usr/share/doc/package/changelog.gz is permitted but deprecated.

It seems that the sentence in this PR, which contradicts the above paragraph, should have been removed (but was probably missed).