Remove Homebrew formula

Homebrew core now packages kakoune, and the Linux-specific stuff is now
in Linuxbrew, so there's no reason to keep this formula around anymore.

contrib/kakoune.rb

@@ -1,21 +0,0 @@
-class Kakoune < Formula
-  homepage "https://github.com/mawww/kakoune"
-  head "https://github.com/mawww/kakoune.git"
-
-  depends_on "docbook-xsl" => :build
-  depends_on "ncurses" => [:build, :recommended]
-  depends_on "asciidoc" => :build
-
-  unless OS.mac?
-    depends_on "libxslt" => :build
-    depends_on "pkg-config" => :build
-  end
-
-  def install
-    ENV["XML_CATALOG_FILES"] = "#{etc}/xml/catalog"
-
-    cd "src" do
-      system "make", "install", "PREFIX=#{prefix}", "debug=no"
-    end
-  end
-end