internal/telemetry/event was renamed to internal/event/core
Some things were partly moved from internal/telemetry/event straight to
internal/event to minimize churn in the following restructuring.
Change-Id: I8511241c68d2d05f64c52dbe04748086dd325158
Reviewed-on: https://go-review.googlesource.com/c/tools/+/229237
Run-TryBot: Ian Cottrell <iancottrell@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>
