Renamed several files in the covidcast signals folder

[tinatownes]

Removed -inactive, and renamed quidel files to distinguish covid and flu.

closes|addresses

Summary:

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

[nmdefries]

The actual changes look good, but I realized that these pages may be linked elsewhere, e.g.. We'd need to update those URLs too to make sure we don't break the links.

Based on the example search results above, this will span multiple repositories, so may be easier for me to do. I think it will affect quidel more than the other pages because the original renaming from, e.g., "safegraph" -> "safegraph-inactive" probably wasn't accompanied by link renaming in other repos.

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
No data about Duplication

See analysis details on SonarCloud

[nmdefries]

Not breaking links to doc pages was easiest by keeping the active (covid) quidel doc file named quidel.md instead of quidel-covid.md; the only other link that needed to be updated was an .../indicator-combination-inactive.html in this repo. No other outdated URLs exist in this repo or other Delphi repos.