fix: Events created from exception shouldnt have top-level message attribute

[kamilogorek]

If the event object has a message attribute, that’s used as the fingerprint, unless user overrides it.
This means, that code like throw new Error("user " + user_id + " had an error") will create a separate group for every user, despite being the very same error (with same stacktrace etc.).

In the @sentry/browser we have it set up correctly, and there's no message for Error based events:

return {
  exception: {
    values: [exception],
  },
};

however, in the node, we do have it different:

return {
  exception: {
    values: [exception],
  },
  message: `${name}: ${error.message || '<no message>'}`,
};

In short, the same code (throw new Error("user " + user_id + " had an error"), say) will result in logical grouping in sentry-js but no grouping in sentry-node.

Removing message will as Daniel pointed out create a new group, but everything else will work, as for exceptions, the message is rendered in the Sentry using type + value values from the exception object.

[getsentry-bot]

	Warnings
⚠️	Please add a changelog entry for your changes.

	Messages
📖	✅ TSLint passed
📖	@sentry/browser gzip'ed minified size: 22.1855 kB

Generated by 🚫 dangerJS

[HazAT]

This will create new groups, not sure how to proceed here.
Major bump just for this is hard, maybe making users aware that this will create new groups?

[mitsuhiko]

I’m conflicted. It sounds like a major bump would be the right thing.

[HazAT]

@kamilogorek Can you add a 5.0.0 section to the changelog and merge this.
I've created a new branch called major/5 which should have all changes for the next major release.

If you added the changelog, feel free to merge it into this branch, I will create a PR to master afterward to track the major release.