ref(nextjs): Don't use Sentry Webpack Plugin in dev mode

[lforst]

Because we're now using Next.js source map resolving server for dev mode we don't need to run the webpack plugin at all in dev mode to get resolved stack traces.

If the plugin isn't silenced in the options it is extremely noisy in dev mode without doing anything. This PR fixes that.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	20.97 KB (-0.35% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	65.48 KB (-0.28% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.51 KB (-0.4% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	57.94 KB (-0.31% 🔽)
@sentry/browser - Webpack (gzipped + minified)	21.11 KB (-0.35% 🔽)
@sentry/browser - Webpack (minified)	68.89 KB (-0.26% 🔽)
@sentry/react - Webpack (gzipped + minified)	21.14 KB (-0.35% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	48.98 KB (-0.15% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.54 KB (-0.27% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.77 KB (-0.3% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	45.35 KB (+0.01% 🔺)
@sentry/replay - Webpack (gzipped + minified)	39.28 KB (0%)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	64.22 KB (-0.12% 🔽)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	57.19 KB (-0.13% 🔽)