core, core/vm, eth/filters: move Removed field into vm.Log

This field used to be assigned by the filter system and returned through
the RPC API. Now that we have a Go client that uses the underlying type,
the field needs to move. It is now assigned to true when the RemovedLogs
event is generated so the filter system doesn't need to care about the
field at all.

While here, remove the log list from ChainSideEvent. There are no users
of this field right now and any potential users could subscribe to
RemovedLogsEvent instead.