[ruby/irb] Simplify command method definition

(https://github.com/ruby/irb/pull/559)

* Remove unnecessary command argument generation code

Now that all the supported Ruby versions handle splat args and splat kwargs,
we don't need that args generation code anymore.

* Remove unused command definition code

If we look at `@EXTEND_COMMANDS`, all commands are defined in a file, which
means the `if load_file` branch is always executed. Therefore we can drop
the else branch of that condition.

* Avoid defining unnecessary command methods

There's no need to define another command method just to call `Command.execute`.

0 files changed, 0 insertions, 0 deletions