Remove defunct conference sites (en)

Closes ruby#1958

Co-authored-by: Jacob Herrington <jacobherringtondeveloper@gmail.com>

Author: stomar

en/community/conferences/index.md

@@ -37,12 +37,6 @@ event dates, location, CFP (Call For Proposals) and Registration information.
   including Armin Roehrl and Michael Neumann, EuRuKo emerged as the
   second annual Ruby event, starting two years after RubyConf.
 
-[Open Source Developer Conference][5]
-: This is an annual open source development conference that is held each
-  year in Australia. While not specifically a Ruby conference, each year
-  we do get a number of Ruby papers and we are always interested in more
-  Ruby content.
-
 ### Regional Ruby Conferences
 
 [Ruby Central][2] administers a [Regional Conference Grant Program][6],
@@ -59,19 +53,8 @@ Virginia, Maryland, and Washington, DC areas.
 Ruby on Rails. The Chicago-based conference has served the Ruby
 community since 2008.
 
-[Madison Ruby][15]: Madison, WI
-
 [Steel City Ruby][16]: Pittsburg, PA
 
-[Ruby on Ales][17] is an annual two-day conference inspired by Ruby, microbrews,
-and snow. Listen to engaging speakers, enjoy delicious food and enjoy the
-wonderful scenery around Bend Oregon.
-
-[Burlington Ruby Conference][18]: A summertime Ruby conference that happens
-annually in Burlington, VT. The conference is two days long and follows a
-single track. The focus of the conference is on creating an environment to
-learn, have fun and meet fellow Rubyists.
-
 [GoRuCo][19]: New York City's annual Ruby conference. A one-day single-track conference.
 
 [DeccanRubyConf][20]: Pune's (India) annual Ruby conference,
@@ -95,7 +78,6 @@ O’Reilly), and Canada on Rails.
 [2]: http://rubycentral.org
 [3]: http://rubykaigi.org/
 [4]: http://euruko.org
-[5]: http://www.osdc.com.au/
 [6]: http://rubycentral.org/community/grant
 [7]: http://www.svforum.org
 [8]: http://rubynation.org/
@@ -105,9 +87,6 @@ O’Reilly), and Canada on Rails.
 [12]: http://www.railsconf.org
 [13]: http://europe.railsconf.org
 [14]: http://www.skillsmatter.com
-[15]: http://madisonruby.org/
 [16]: http://steelcityruby.org/
-[17]: http://ruby.onales.com/
-[18]: http://burlingtonrubyconference.com
 [19]: http://goruco.com/
 [20]: http://www.deccanrubyconf.org/