ref(replay): Explicitly clear eventBuffer for checkout events

[mydea]

This too is a partial extraction of #7025, to prepare for this & break this up in multiple parts.

This will make it easier in a follow up step to handle clearing a bit different when in buffer mode, to keep more data in store.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	21.02 KB (-0.01% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	65.66 KB (0%)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	19.56 KB (+0.01% 🔺)
@sentry/browser - ES6 CDN Bundle (minified)	58.12 KB (0%)
@sentry/browser - Webpack (gzipped + minified)	21.17 KB (0%)
@sentry/browser - Webpack (minified)	69.07 KB (0%)
@sentry/react - Webpack (gzipped + minified)	21.19 KB (0%)
@sentry/nextjs Client - Webpack (gzipped + minified)	49.04 KB (0%)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.6 KB (-0.01% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	26.83 KB (-0.01% 🔽)
@sentry/replay ES6 CDN Bundle (gzipped + minified)	46.87 KB (+0.15% 🔺)
@sentry/replay - Webpack (gzipped + minified)	40.67 KB (+0.19% 🔺)
@sentry/browser + @sentry/tracing + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	65.69 KB (+0.1% 🔺)
@sentry/browser + @sentry/replay - ES6 CDN Bundle (gzipped + minified)	58.64 KB (+0.13% 🔺)