2.0 packages being removed from avalon

[Justin C. Sherrill]

Since 2.4 is out, and we'll have binary pkgsrc packages for it soon, the
2.0 packages are due to be removed.  If this will cause you trouble,
please speak up.

The plan is to keep packages for the current release (2.4) and the
previous release (2.2), which gives us a binary package retention schedule
of about a year.

(The 2.3.1 packages on avalon.dragonflybsd.org currently work for 2.4, and
the directories are symlinked in until a 2.4 build is finished.)