Hide debugger hint after the input is submitted

If `output_modifier_proc`'s `complete` arg is true, it means the input is
submitted. In that case, debugger hint doesn't provide value to users
and adds noise to the output. So we hide it in such case.

lib/irb/debug.rb

@@ -65,7 +65,7 @@ def DEBUGGER__.capture_frames(*args)
               cmd = output.split(/\s/, 2).first
 
               if DEBUGGER__.commands.key?(cmd)
-                output = output.sub(/\n$/, " # debug command\n")
+                output = output.sub(/\n$/, " # debug command\n") unless complete
               end
             end