ref(tracing): Don't track transaction sampling method

[AbhiPrasad]

In our initial work on Dynamic Sampling (#3068), we added the ability to track transaction sampling method.

https://github.com/getsentry/sentry-javascript/pull/3068/files#diff-337facb22f742f05b3326aed66ca6b0d5eb9c782c7c03c88ef0170fd97dc410dR104-R109

export enum TransactionSamplingMethod {
  Explicit = 'explicitly_set',
  Sampler = 'client_sampler',
  Rate = 'client_rate',
  Inheritance = 'inheritance',
}

To use this info, we set the transaction sampling method and sample rate on the transaction event header:

sample_rates: [{ id: samplingMethod, rate: sampleRate }],

In Relay this is used here: https://github.com/getsentry/relay/blob/4b16d279ccf21d3c1d975b652ffca01ebd72a500/relay-general/src/protocol/metrics.rs#L7-L16

This is no longer needed for dynamic sampling context with the introduction of Dynamic Sampling Context, so we can remove this code.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.47 KB (-0.21% 🔽)
@sentry/browser - ES5 CDN Bundle (minified)	60.16 KB (-0.18% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.06 KB (-0.23% 🔽)
@sentry/browser - ES6 CDN Bundle (minified)	53.08 KB (-0.21% 🔽)
@sentry/browser - Webpack (gzipped + minified)	19.85 KB (-0.2% 🔽)
@sentry/browser - Webpack (minified)	64.49 KB (-0.17% 🔽)
@sentry/react - Webpack (gzipped + minified)	19.88 KB (-0.2% 🔽)
@sentry/nextjs Client - Webpack (gzipped + minified)	44.73 KB (-0.21% 🔽)
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	25.93 KB (-0.37% 🔽)
@sentry/browser + @sentry/tracing - ES6 CDN Bundle (gzipped + minified)	24.33 KB (-0.37% 🔽)