JLine 3: resolve status of `edit` command

[SethTisue]

commented-out code in the PR:

    // TODO maybe just drop these commands, as jline subsumes them
     //cmd("edit", "<id>|<line>", "edit history", editCommand),

[SethTisue]

@lrytz wrote:

@dwijnand notes that jshell has an edit command that actually works reliably and is useful. though it's more relevant in java given it's verbosity. our edit works or not if you're lukcy.

[SethTisue]

@dwijnand wrote:

Details: in jshell /edit works with my settings of EDITOR=vim while with scala I need to set EDITOR=mvim to have something that works.

[SethTisue]

out of scope for Scala 2