fix(networkmanager): Remove header 'cookie' from request hash

[DonoA]

This fixes an issue in which a response may not be recorded or trigger an event because of differing cookie headers from the request.

I didn't see anywhere to add testing for this functionality, however if you would like tests added, just point me in the right direction.

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[DonoA]

I signed it!

[googlebot]

CLAs look good, thanks!

[aslushnikov]

Thanks. I'll add a test for this in a follow-up.