Remove IRB::NotImplementedError

[tompng]

NotImplementedError is defined globally, and can be used as raise NotImplementedError
But inside IRB module, raise NotImplementedError raises ArgumentError.

irb(main):001* module IRB
irb(main):002*   raise NotImplementedError
irb(main):003> end
gems/irb-1.11.2/lib/irb/lc/ja/error.rb:16:in `initialize': wrong number of arguments (given 0, expected 1) (ArgumentError)

Remove IRB::NotImplementedError and IRB::OutputMethod::NotImplementedError because we don't need it.

[st0012]

I didn't know IRB has a NotImplementedError 🤯

Should we remove this version and make the JA version simply inherit Ruby's NotImplementedError?

[tompng]

I want to leave it to reduce difference between locale and possibility of locale dependent bug.

[st0012]

Actually, I think we don't need a locale-friendly version of NotImplementedError because it's an exception that target IRB developers instead of end users. So I prefer dropping IRB::NotImplementedError completely.

[tompng]

Makes sense.
I Removed class NotImplementedError defined in IRB.

[st0012]

Nice cleanup 👍