Don't require io/wait on Ruby 3.2 and higher (#61)

io/wait functionality has been in core Ruby since 3.2 and prior to that
was a default gem. With the "1.0.0" release of io-wait it is now
deprecated and warns when loaded. This patch removes the last reference
to the io/wait library to avoid deprecation warnings.

See ruby/io-wait#79 and ruby/io-wait#80

Author: headius

lib/drb/drb.rb

@@ -41,7 +41,7 @@
 #   Translation of presentation on Ruby by Masatoshi Seki.
 
 require 'socket'
-require 'io/wait'
+require 'io/wait' if RUBY_VERSION < '3.2'
 require 'monitor'
 require_relative 'eq'
 require_relative 'version'