Add the call of DropKids at the end of executor.Run to delete the local scopes created in operators

[Xreki]

No description provided.

[jacquesqiao]

if create_vars is False and create_local_scope is True, do we need to use

local_scope->DropKids()

?

[Xreki]

The local_scope itself is deleted by scope->DeleteScope(local_scope);, all the kids will be deleted, see the implementation of the destructor:

Paddle/paddle/fluid/framework/scope.cc

Lines 37 to 43 in 0285a2b

	Scope::~Scope() {
	DropKids();
	for (auto& kv : vars_) {
	VLOG(3) << "Destroy variable " << kv.first;
	delete kv.second;
	}
	}

[Yancey1989]

Hi @Xreki , maybe we can't delete the kids in the execute function, some conditions like dist training, pserver will execute the optimize blocks on the same scope instead of a new scope for each optimizes action.

related issued #10625

[jacquesqiao]

LGTM!