The Subscription type is gone, all uses are replaced by
*TypeMuxSubscription. This change is prep-work for the
introduction of the new Subscription type in a later commit.
gorename -from '"github.com/ethereum/go-ethereum/event"::Event' -to TypeMuxEvent
gorename -from '"github.com/ethereum/go-ethereum/event"::muxsub' -to TypeMuxSubscription
gofmt -w -r 'Subscription -> *TypeMuxSubscription' ./event/*.go
find . -name '*.go' -and -not -regex '\./vendor/.*' \| xargs gofmt -w -r 'event.Subscription -> *event.TypeMuxSubscription'