internal/trace: remove unused StateTransition.id field

Change-Id: I6a6a69647e6d91f9fd937032d95cbaf5d737fd5d
Reviewed-on: https://go-review.googlesource.com/c/go/+/694619
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: David Chase <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>
Auto-Submit: Michael Knyszek <[email protected]>

Author: felixge

src/internal/trace/resources.go

@@ -224,7 +224,6 @@ type StateTransition struct {
 
 	// The actual transition data. Stored in a neutral form so that
 	// we don't need fields for every kind of resource.
-	id       int64
 	oldState uint8
 	newState uint8
 }