irb:rdbg cleanups (#697)

* Remove unused method and constant from IRB::Debug

* Update comments

lib/irb.rb

@@ -439,9 +439,9 @@ def initialize(workspace = nil, input_method = nil)
       @scanner = RubyLex.new(@context)
     end
 
-    # A hook point for `debug` command's TracePoint after :IRB_EXIT as well as its clean-up
+    # A hook point for `debug` command's breakpoint after :IRB_EXIT as well as its clean-up
     def debug_break
-      # it means the debug command is executed
+      # it means the debug integration has been activated
       if defined?(DEBUGGER__) && DEBUGGER__.respond_to?(:capture_frames_without_irb)
         # after leaving this initial breakpoint, revert the capture_frames patch
         DEBUGGER__.singleton_class.send(:alias_method, :capture_frames, :capture_frames_without_irb)
@@ -547,14 +547,13 @@ def eval_input
       each_top_level_statement do |statement, line_no|
         signal_status(:IN_EVAL) do
           begin
-            # If the integration with debugger is activated, we need to handle certain input differently
+            # If the integration with debugger is activated, we return certain input if it should be dealt with by debugger
             if @context.with_debugger && statement.should_be_handled_by_debugger?
               return statement.code
             end
 
             @context.evaluate(statement.evaluable_code, line_no)
 
-            # Don't echo if the line ends with a semicolon
             if @context.echo? && !statement.suppresses_echo?
               if statement.is_assignment?
                 if @context.echo_on_assignment?

lib/irb/debug.rb

@@ -2,10 +2,6 @@
 
 module IRB
   module Debug
-    BINDING_IRB_FRAME_REGEXPS = [
-      '<internal:prelude>',
-      binding.method(:irb).source_location.first,
-    ].map { |file| /\A#{Regexp.escape(file)}:\d+:in `irb'\z/ }
     IRB_DIR = File.expand_path('..', __dir__)
 
     class << self
@@ -76,14 +72,6 @@ def configure_irb_for_debugger(irb)
         irb.context.irb_name += ":rdbg"
       end
 
-      def binding_irb?
-        caller.any? do |frame|
-          BINDING_IRB_FRAME_REGEXPS.any? do |regexp|
-            frame.match?(regexp)
-          end
-        end
-      end
-
       module SkipPathHelperForIRB
         def skip_internal_path?(path)
           # The latter can be removed once https://github.com/ruby/debug/issues/866 is resolved