events: improve creation time of EventTarget

Benchmarks

may not be accurate until https://github.com/nodejs/build/issues/3657#issuecomment-204153499 is resolved

Benchmark URL

No change:

23:20:03                                                         confidence improvement accuracy (*)   (**)  (***)
23:20:03 events/eventtarget-add-remove.js nListener=10 n=1000000                 0.01 %       ±0.63% ±0.84% ±1.10%
23:20:03 events/eventtarget-add-remove.js nListener=5 n=1000000                  0.31 %       ±0.52% ±0.69% ±0.90%
23:20:03 events/eventtarget-creation.js n=1000000                               -0.59 %       ±2.34% ±3.11% ±4.04%
23:20:03 events/eventtarget.js listeners=1 n=1000000                            -0.26 %       ±0.38% ±0.51% ±0.66%
23:20:03 events/eventtarget.js listeners=10 n=1000000                            0.25 %       ±0.38% ±0.50% ±0.66%
23:20:03 events/eventtarget.js listeners=5 n=1000000                            -0.34 %       ±0.94% ±1.25% ±1.63%
23:20:03