[ruby/irb] Remove dead doc (https://github.com/ruby/irb/pull/819)

https://github.com/ruby/irb/commit/2d5a1afdf5

lib/irb.rb

@@ -705,12 +705,6 @@ require_relative "irb/pager"
 # Command-line option <tt>-W[_level_]<tt>
 # sets warning level; 0=silence, 1=medium, 2=verbose.
 #
-# :stopdoc:
-# === Performance Measurement
-#
-# IRB.conf[:MEASURE] IRB.conf[:MEASURE_CALLBACKS] IRB.conf[:MEASURE_PROC]
-# :startdoc:
-#
 # == Other Features
 #
 # === Load Modules
@@ -771,12 +765,6 @@ require_relative "irb/pager"
 #
 # Note that the configuration file entry overrides the command-line options.
 #
-# :stopdoc:
-# === \Context Mode
-#
-# IRB.conf[:CONTEXT_MODE]
-# :startdoc:
-#
 # === \IRB Name
 #
 # You can specify a name for \IRB.
@@ -815,12 +803,6 @@ require_relative "irb/pager"
 # Each time the configuration is changed,
 # that proc is called with argument +conf+:
 #
-# :stopdoc:
-# === \Locale
-#
-# IRB.conf[:LC_MESSAGES]
-# :startdoc:
-#
 # === Encodings
 #
 # Command-line option <tt>-E _ex_[:_in_]</tt>