ref: Remove user segment

[lforst]

Removes the unused user segment API from the User interface and setUser.

Allows us to clean up a few things with regards to DSC and scopes <3

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	78.16 KB (-0.22% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.37 KB (-0.29% 🔽)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	73.31 KB (-0.25% 🔽)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	63.01 KB (-0.26% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.35 KB (-0.5% 🔽)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.22 KB (-0.51% 🔽)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.2 KB (-0.54% 🔽)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.21 KB (-0.53% 🔽)
@sentry/browser - Webpack (gzipped)	22.48 KB (-0.69% 🔽)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	76.19 KB (-0.23% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.71 KB (-0.28% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.47 KB (-0.56% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.56 KB (-0.7% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	213.68 KB (-0.19% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.48 KB (-0.39% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	73.86 KB (-0.54% 🔽)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.64 KB (-0.44% 🔽)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.76 KB (-0.24% 🔽)
@sentry/react - Webpack (gzipped)	22.52 KB (-0.66% 🔽)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.33 KB (-0.26% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	51.52 KB (-0.41% 🔽)
@sentry-internal/feedback - Webpack (gzipped)	17.2 KB (-0.1% 🔽)