lib: micro-optimize EventEmitter#removeListener()

[bnoordhuis]

Replace the call to Array#splice() with a faster open-coded version
that creates less garbage.

Add a new benchmark to prove it. With the change applied, it scores
a whopping 40% higher.

R=@chrisdickinson

[sonewman]

👍

[algesten]

That's super sweet!

Perhaps a pedantic point, but shouldn't we call it something else but splice though? I mean since it does one very specific thing. shiftOne?

[chrisdickinson]

LGTM. I looked into splitting splice into spliceFront and spliceBack (copying backwards or forwards from the splice position, respectively) but since the usual number of listeners is <= 10, it didn't make too much of a difference. I also tried specializing position == 0 and position == list.length, but again, no difference!

[bnoordhuis]

Cheers, fixed up the indentation and (partially) incorporated @algesten's feedback by renaming the function to spliceOne(). Landed in d3f8db1.

@chrisdickinson Using Array#shift() to remove the first element is a bit faster, but only for larger lists. The lower bound is probably at least 16 elements but there doesn't seem to be an appreciable difference until the array length is in the low hundreds.