ref(core): Remove unnecessary nested dropUndefinedKeys call

[Lms24]

This very small PR removes an unnecessary nested call to dropUndefinedKeys which we don't need because the function is already recursive (which could be causing a problem).

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.32 KB (-4.05% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	59.89 KB (-7.31% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.18 KB (-3.63% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	53.58 KB (-7.58% 🔽)
@sentry/browser - Webpack (gzipped + minified)	19.87 KB (-14.5% 🔽)
@sentry/browser - Webpack (minified)	63.02 KB (-22.88% 🔽)
@sentry/react - Webpack (gzipped + minified)	19.89 KB (-14.54% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	43.71 KB (-9.04% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.34 KB (-2.81% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	23.9 KB (-2.4% 🔽)