Missing from the Changelog's sources and signals is google-symptoms

[tinatownes]

google-symptoms https://cmu-delphi.github.io/delphi-epidata/api/covidcast-signals/google-symptoms.html is an active source that is not listed in the changelog at https://cmu-delphi.github.io/delphi-epidata/api/covidcast_changelog.html.

[JavierMtzRdz]

In PR #1702, the changelog was moved to its corresponding pages as discussed in #1654. For google-symptoms, it is here now.