remove the metrics sender

[nlf]

the metrics sender as it is today defaults to disabled and contains only incredibly minimal value anyway. we should just remove it, we can always revisit the intended purpose later and come up with a better solution.

[npm-deploy-user]

	angular-quickstart			app-large			app-medium			ember-quickstart			react-app
	prev	current	status	prev	current	status	prev	current	status	prev	current	status	prev	current	status
initial install	41s	40.3s	✅	39.5s	47.7s	🛑	34.5s	33.7s	✅	28.1s	26.2s	✅	33.5s	34.3s	✅🐌
repeat install	9.6s	2.7s	✅	8.6s	3s	✅	8.3s	2.7s	✅	7.7s	1.4s	✅	9.1s	2.7s	✅
with warm cache	32.3s	26.3s	✅	33.8s	27.7s	✅	31.3s	18.3s	✅	23.4s	17.5s	✅	29.1s	18.8s	✅
with node_modules	9.2s	5.4s	✅	8.6s	4.4s	✅	9s	3.4s	✅	7.8s	1.9s	✅	9.4s	5.5s	✅
with lockfile	32.6s	27.7s	✅	31s	29.2s	✅	29s	20.2s	✅	21.7s	17.3s	✅	27.4s	24.4s	✅
with warm cache and node_modules	9.3s	3.3s	✅	7.9s	3.5s	✅	8.4s	2.9s	✅	7.6s	1.8s	✅	9.2s	2.9s	✅
with warm cache and lockfile	24.7s	9.5s	✅	26.3s	12.7s	✅	24.3s	7.6s	✅	17.8s	6.4s	✅	21.3s	7.9s	✅
with node_modules and lockfile	10.1s	5.1s	✅	9.8s	4.5s	✅	8.6s	3.2s	✅	7.8s	1.7s	✅	9.7s	5.7s	✅

[isaacs]

Looks good, but wanna remove from docs, too?

docs/content/using-npm/config.md:#### metrics-registry
docs/content/using-npm/config.md:The registry you want to send cli metrics to if `send-metrics` is true.
docs/content/using-npm/config.md:#### send-metrics
docs/content/using-npm/config.md:If true, success/failure metrics will be reported to the registry stored in
docs/content/using-npm/config.md:`metrics-registry`.  These requests contain the number of successful and
docs/content/using-npm/registry.md:  This is used to gather better metrics on how npm is used by humans, versus

[nlf]

Looks good, but wanna remove from docs, too?

docs/content/using-npm/config.md:#### metrics-registry
docs/content/using-npm/config.md:The registry you want to send cli metrics to if `send-metrics` is true.
docs/content/using-npm/config.md:#### send-metrics
docs/content/using-npm/config.md:If true, success/failure metrics will be reported to the registry stored in
docs/content/using-npm/config.md:`metrics-registry`.  These requests contain the number of successful and
docs/content/using-npm/registry.md:  This is used to gather better metrics on how npm is used by humans, versus

i removed the mentions in the config doc, but the registry doc looks like it actually refers to the headers sent as part of requests rather than this particular metrics gatherer so i left that alone