This commit removes the references to the Big Tent from the project list
slides. We're trying to move away from that term because it causes
confusion to a lot of people. Instead we should call them OpenStack
projects. One note about big tent is left in, because people still use
the term, but we should use that to explain it's the old way to describe
all OpenStack projects.
Change-Id: Ifea66e1dae9c4e644e3efa70c0be0526b24d41cc
986dc5aee4