Remove enable tracing from android sample manifest

[lbloder]

#skip-changelog

📜 Description

Remove the io.sentry.traces.enable meta-data from AndroidManifest.xml in the Android Sample.
Update description of io.sentry.traces.sample-rate.

💡 Motivation and Context

enableTracing has been removed in v8, therefore the io.sentry.traces.enable value in the AndroidManifest.xml has no effect and needs to be removed to not cause confusion or users.

💚 How did you test it?

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• No new PII added or SDK only sends newly added PII if sendDefaultPII is enabled.
• I updated the docs if needed.
• Review from the native team if needed.
• No breaking change or entry added to the changelog.
• No breaking change for hybrid SDKs or communicated to hybrid SDKs.

🔮 Next steps