Remove the 'still in testing' status lines once 1.0 and Switchify 3.1 are stable #1079

When Switchify PC 1.0 is released and Switchify 3.1 is on Google Play, remove the status sentence added in #1078:

Built-in PC control arrives with Switchify 3.1, which is still in testing and not yet on Google Play; Switchify PC 1.0 is a release candidate.

grep -rn "still in testing" site/ finds every copy. The same sentence lives on www.theswitchify.app (switchify-website PR #21) and in the Android docs (switchify-android #2981); remove those in the same sweep, along with the "release candidate" wording on www.