Here's a "Tiny Desk" concert of four songs from the Broadway show, Wicked. Stephen Schwartz (who wrote the songs) is at the piano. The two vocalists are Alyssa Fox and McKenzie Kurtz — two of the 43,046 actresses who've played Elphaba and/or Glinda since this show opened in New York on October 30, 2003. So far, it's had about 7,890 performances at the Gershwin Theater in New York. This is a lot…