Remove `require 'io/wait'` where it's no longer necessary. (#6932)

* Remove `require 'io/wait'` as it's part of core now.

* Update ruby specs using version gates.

* Add note about why it's conditional.

3 files changed, 3 insertions, 6 deletions

diff --git a/test/io/wait/test_io_wait.rb b/test/io/wait/test_io_wait.rb
index 8a2b6c2d12..7997a4814f 100644
--- a/test/io/wait/test_io_wait.rb
+++ b/test/io/wait/test_io_wait.rb
@@ -3,10 +3,9 @@
 require 'test/unit'
 require 'timeout'
 require 'socket'
-begin
-  require 'io/wait'
-rescue LoadError
-end
+
+# For `IO#ready?` and `IO#nread`:
+require 'io/wait'
 
 class TestIOWait < Test::Unit::TestCase
 
diff --git a/test/io/wait/test_io_wait_uncommon.rb b/test/io/wait/test_io_wait_uncommon.rb
index 7b92e4c758..0f922f4e24 100644
--- a/test/io/wait/test_io_wait_uncommon.rb
+++ b/test/io/wait/test_io_wait_uncommon.rb
@@ -1,6 +1,5 @@
 # frozen_string_literal: true
 require 'test/unit'
-require 'io/wait'
 
 # test uncommon device types to check portability problems
 # We may optimize IO#wait_*able for non-Linux kernels in the future
diff --git a/test/io/wait/test_ractor.rb b/test/io/wait/test_ractor.rb
index 3742680cf7..800216e610 100644
--- a/test/io/wait/test_ractor.rb
+++ b/test/io/wait/test_ractor.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 require 'test/unit'
 require 'rbconfig'
-require 'io/wait'
 
 class TestIOWaitInRactor < Test::Unit::TestCase
   def test_ractor