feat(utils): kill unused promise buffer api

[mitsuhiko]

Remove some unused public API.

[JonasBa]

Ah, good catch on remove. I didnt want to actually expose the underlying array, just to make sure nobody can use it, but I guess since it should only be used by us, it's ok.

[mitsuhiko]

Yeah I wanted to not expose this at all, but due to how the tests are structured that was the only way to get rid of the length api.

[github-actions]

size-limit report

Path	Base Size (7f1fe2d)	Current Size	Change
@sentry/browser - CDN Bundle (gzipped)	20.35 KB	20.35 KB	-0.02% 🔽
@sentry/browser - CDN Bundle (minified)	64.99 KB	64.96 KB	-0.06% 🔽
@sentry/browser - Webpack	22.35 KB	22.33 KB	-0.08% 🔽
@sentry/browser - Webpack - gzip = false	76.5 KB	76.47 KB	-0.06% 🔽
@sentry/react - Webpack	22.38 KB	22.37 KB	-0.07% 🔽
@sentry/nextjs Client - Webpack	46.49 KB	46.48 KB	-0.02% 🔽
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	28.51 KB	28.5 KB	-0.04% 🔽