[ruby/irb] Remove misleading documentation

(https://github.com/ruby/irb/pull/906)

https://github.com/ruby/irb/issues/904

https://github.com/ruby/irb/commit/89bca01bba

lib/irb.rb

@@ -145,7 +145,6 @@ require_relative "irb/pager"
 # *   The value of variable `$XDG_CONFIG_HOME/irb/irbrc`, if defined.
 # *   File `$HOME/.irbrc`, if it exists.
 # *   File `$HOME/.config/irb/irbrc`, if it exists.
-# *   File `.config/irb/irbrc` in the current directory, if it exists.
 # *   File `.irbrc` in the current directory, if it exists.
 # *   File `irb.rc` in the current directory, if it exists.
 # *   File `_irbrc` in the current directory, if it exists.