ref(browser): Remove sendBeacon API usage

[AbhiPrasad]

Since we use keepalive anyway as default in our fetch transport, let's remove all usage for the sendBeacon API.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.43 KB (-0.49% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	63.6 KB (-0.39% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.11 KB (-0.38% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	56.7 KB (-0.4% 🔽)
@sentry/browser - Webpack (gzipped + minified)	21.59 KB (-0.33% 🔽)
@sentry/browser - Webpack (minified)	71.78 KB (-0.48% 🔽)
@sentry/react - Webpack (gzipped + minified)	21.62 KB (-0.38% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	51.96 KB (-0.19% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	27.76 KB (-17.8% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.06 KB (-0.26% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	44.23 KB (+0.01% 🔺)
@sentry/replay - Webpack (gzipped + minified)	38.28 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	62.38 KB (-0.11% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	55.93 KB (-0.12% 🔽)

[Lms24]

🚀