feat(transports): trim down some code in the transports

[mitsuhiko]

This removes some code in transports to make it smaller. In particular it removes the DSN validation for debug builds.

[github-actions]

size-limit report

Path	Base Size (fb87d34)	Current Size	Change
@sentry/browser - CDN Bundle (gzipped)	21.17 KB	21.04 KB	-0.61% 🔽
@sentry/browser - CDN Bundle (minified)	67.7 KB	67.23 KB	-0.69% 🔽
@sentry/browser - Webpack	22.79 KB	22.81 KB	+0.09% 🔺
@sentry/browser - Webpack - gzip = false	78.22 KB	78.32 KB	+0.12% 🔺
@sentry/react - Webpack	22.83 KB	22.85 KB	+0.09% 🔺
@sentry/nextjs Client - Webpack	47.33 KB	47.34 KB	+0.03% 🔺
@sentry/browser + @sentry/tracing - CDN Bundle (gzipped)	29.36 KB	29.37 KB	+0.03% 🔺