Make iterator seek target a local variable

[vweevers]

Here:

leveldown/binding.cc

Line 1373 in 55f30a3

NAPI_METHOD(iterator_seek) {

Because that's the only function in which it's used. We don't have to keep it around. Removing the need for this:

leveldown/binding.cc

Lines 559 to 567 in 55f30a3

	void ReleaseTarget () {
	if (target_ != NULL) {
	if (!target_->empty()) {
	delete [] target_->data();
	}
	delete target_;
	target_ = NULL;
	}
	}