core/vm: Refactor tracing to make Tracer the main interface

This CL makes several refactors:
 - Define a Tracer interface, implementing the `CaptureState` method
 - Add the VM environment as the first argument of
   `Tracer.CaptureState`
 - Rename existing functionality `StructLogger` an make it an
   implementation of `Tracer`
 - Delete `StructLogCollector` and make `StructLogger` collect the logs
   directly
 - Change all callers to use the new `StructLogger` where necessary and
   extract logs from that.
 - Deletes the apparently obsolete and likely nonfunctional 'TraceCall'
   from the eth API.

Callers that only wish accumulated logs can use the `StructLogger`
implementation straightforwardly. Callers that wish to efficiently
capture VM traces and operate on them without excessive copying can now
implement the `Tracer` interface to receive VM state at each step and
do with it as they wish.

This CL also removes the accumulation of logs from the vm.Environment;
this was necessary as part of the refactor, but also simplifies it by
removing a responsibility that doesn't directly belong to the
Environment.

core/vm/runtime/env.go

@@ -39,8 +39,6 @@ type Env struct {
 	difficulty *big.Int
 	gasLimit   *big.Int
 
-	logs []vm.StructLog
-
 	getHashFn func(uint64) common.Hash
 
 	evm *vm.EVM
@@ -62,23 +60,11 @@ func NewEnv(cfg *Config, state *state.StateDB) vm.Environment {
 		Debug:     cfg.Debug,
 		EnableJit: !cfg.DisableJit,
 		ForceJit:  !cfg.DisableJit,
-
-		Logger: vm.LogConfig{
-			Collector: env,
-		},
 	})
 
 	return env
 }
 
-func (self *Env) StructLogs() []vm.StructLog {
-	return self.logs
-}
-
-func (self *Env) AddStructLog(log vm.StructLog) {
-	self.logs = append(self.logs, log)
-}
-
 func (self *Env) RuleSet() vm.RuleSet      { return self.ruleSet }
 func (self *Env) Vm() vm.Vm                { return self.evm }
 func (self *Env) Origin() common.Address   { return self.origin }