Revert "[cobalt-fidl] Add new CobaltEvent methods"

This reverts commit 95288e7e.

Reason for revert: causing build failure in higher layers, see
e.g. https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket.appspot.com/8926667935749990112/+/steps/build/0/steps/build_fuchsia/0/steps/ninja/0/stdout

Original change's description:
> [cobalt-fidl] Add new CobaltEvent methods
> 
> This will alow us to support multiple events at once as well as
> multiple event codes per event.
> 
> CB-197
> 
> Test: No functional changes, CQ
> Change-Id: Ifaf2f1ddf19a9f87299deff88692413208daafee

TBR=rudominer@google.com,azani@google.com,zmbush@google.com

Change-Id: I60cad9e595abe3ec4de7ee59fe2600c934a7cdb8
No-Presubmit: true
No-Tree-Checks: true
No-Try: true