Remove count field from filebeat event

[ruflin]

This closes #778

Remove count as required field from system tests checks

[tsg]

LGTM.

[ruflin]

@andrewkroh I didn't check in detail why, but it seems like the EnsureField functions don't work as expected as I didn't change it: https://github.com/elastic/beats/blob/master/libbeat/common/mapstr.go#L91-L91 I assume the reason is that a copy and not a reference is passed, so the copy is modified. Perhaps we should have a closer look at this in an other PR?

[andrewkroh]

The method is written correctly (maps are passed by reference). It just isn't called in libbeat (anymore?). To my surprise it's only invoked by Packetbeat.

[ruflin]

@andrewkroh Will you have a look at that?

[andrewkroh]

I don't think there is anything to look into. I think that is the behavior we want because this means count is not required to be included in the data produced by all Beats.

[tsg]

Yes, I think @urso moved the check for it to Packetbeat.