Delete adium-nightly.rb (#3881)

Both the `homepage` and `url` are dead.

Casks/adium-nightly.rb

@@ -1,16 +0,0 @@
-cask 'adium-nightly' do
-  version '1.6hgr5946'
-  sha256 'aa5f92647a256fff0b5098679bd4966db039769a0e8a094116fd06b0cb3dcfc2'
-
-  url "http://nightly.adium.im/adium-adium-1.6/Adium_#{version}.dmg"
-  name 'Adium'
-  homepage 'http://nightly.adium.im/?repo_branch=adium-adium-1.6'
-
-  app 'Adium.app'
-
-  zap delete: [
-                '~/Library/Caches/Adium',
-                '~/Library/Caches/com.adiumX.adiumX',
-                '~/Library/Preferences/com.adiumX.adiumX.plist',
-              ]
-end