fix: remove unused lib/npm relics

[lukekarrys]

npm being an instance of EventEmitter and have a tmp public getter
were both unused. Since we do not have a public API we can make these
changes without it being a breaking change.

[npm-cli-bot]

found 1 benchmarks with statistically significant performance regressions

• app-medium: clean

timing results

app-large	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit	show-version	run-script
npm@9	42.761 ±4.91	14.717 ±0.09	14.448 ±0.02	16.634 ±0.69	2.519 ±0.19	2.429 ±0.02	1.989 ±0.01	9.901 ±0.07	2.015 ±0.01	3.189 ±0.21	0.352 ±0.00	0.365 ±0.00
#6482	45.056 ±9.57	14.961 ±0.12	14.612 ±0.09	17.081 ±0.91	2.542 ±0.14	2.472 ±0.08	2.045 ±0.02	10.161 ±0.09	2.047 ±0.04	3.140 ±0.09	0.358 ±0.01	0.377 ±0.00

app-medium	clean	lock-only	cache-only	cache-only peer-deps	modules-only	no-lock	no-cache	no-modules	no-clean	no-clean audit	show-version	run-script
npm@9	26.834 ±0.71	11.492 ±0.11	11.188 ±0.07	12.035 ±0.17	2.189 ±0.01	2.172 ±0.01	2.031 ±0.01	7.588 ±0.05	1.909 ±0.00	2.708 ±0.05	0.352 ±0.01	0.367 ±0.01
#6482	33.741 ±3.36	11.721 ±0.04	11.359 ±0.09	12.045 ±0.29	2.211 ±0.03	2.212 ±0.01	2.047 ±0.01	7.622 ±0.08	1.947 ±0.01	2.721 ±0.05	0.356 ±0.01	0.374 ±0.01