Don't show 'Maybe IRB bug!' in show_source and ls command

[tompng]

ls command shows Maybe IRB bug! when eval fails.

irb(main):001> ls foo
undefined local variable or method `foo' for main (NameError)
[backtraces]
Maybe IRB bug!

irb(main):001> ls raise(Exception)
Exception (Exception)
[backtraces]
Maybe IRB bug!

irb(main):001> ls (1.."a")
bad value for range (ArgumentError)
[backtraces]
Maybe IRB bug!

Same for show_source

irb(main):001> show_source (1.."a").itself
bad value for range (ArgumentError)
Maybe IRB bug!

irb(main):001> show_source raise(Exception).itself
Exception (Exception)
Maybe IRB bug!

This pull request fixes it.

irb(main):001> ls foo
NameError: undefined local variable or method `foo' for main
irb(main):002> ls raise(Exception,'aa')
Exception: aa
irb(main):003> ls Integer, grep: /#{raise Exception,'bb'}/
Exception: bb
irb(main):004> show_source raise(Exception,'aa').itself
Error: Couldn't locate a definition for raise(Exception,'aa').itself

The use of args, kwargs = ruby_args(arg) (in legacy ls format) is also removed.

[st0012]

Thx 👍