Dont set lastEventId for transactions

[marandaneto]

lastEventId could be used for reporting a userfeedback, so we cant assign the lastEventId for transactions

Spec PR https://github.com/getsentry/develop/pull/430/files

Have to change in all the SDKs that do it

• Dart

[marandaneto]

@maciejwalkowiak can you check the Java SDK, please?
@brustolin the iOS SDK has to change too.
@bruno-garcia .NET SDK as well
@rhcarvalho for Web SDKs
I'm gonna do it for Flutter

[kamilogorek]

Web: getsentry/sentry-javascript#3966

[bruno-garcia]

The .NET SDK already works as intended. A test to validate the behavior was added: getsentry/sentry-dotnet#1191

[kamilogorek]

Go: getsentry/sentry-go#379

[bruno-garcia]

Java needs fixing:

Here:
https://github.com/getsentry/sentry-java/blob/d3764bfc97eed22564a1e23ba96fa73ad2685498/sentry/src/main/java/io/sentry/Hub.java#L578
And here:
https://github.com/getsentry/sentry-java/blob/d3764bfc97eed22564a1e23ba96fa73ad2685498/sentry/src/main/java/io/sentry/Hub.java#L149-L150

@maciejwalkowiak can you please help us out here?