Move agedu to headonly

The checksum on the tarball is not stable.

Closes Homebrew/homebrew#26671.

Formula/agedu.rb

@@ -1,19 +0,0 @@
-require 'formula'
-
-class Agedu < Formula
-  homepage 'http://www.chiark.greenend.org.uk/~sgtatham/agedu/'
-  url 'http://www.chiark.greenend.org.uk/~sgtatham/agedu/agedu-r10126.tar.gz'
-  version 'r10126'
-  sha1 '4438ae698b626cba5ce061ed3ae5eefa5bfb1c50'
-
-  def install
-    system "./configure", "--disable-debug", "--disable-dependency-tracking",
-                          "--prefix=#{prefix}"
-    system "make install"
-  end
-
-  test do
-    system "#{bin}/agedu", "-s", "."
-    assert File.exist?("agedu.dat")
-  end
-end