find(1): Update date format reference and remove cvs(1) references

cvs(1) is not installed by default. Change the date format reference to
note that find(1) understands ISO8601 and RFC822 date formats. Also
remove references to cvs(1).

PR: 254894
Reported by: danielsh@apache.org

(cherry picked from commit 52dbe1a0f419b8d45b4beed56b90ff48bc12e14c)