remove wasted return statement

[Constellation]

function t() {
  if (a) {
    ...
  }
  return;
}

should be transformed to

function t() {
  if (a) {
    ...
  }
}

function f() {
  return void 0;
}

to

function t() { }

We should check control flow and eliminate wasted return statement.

[Constellation]

Quoted:

function a(a){return void a()}

which would hopefully be further reduced to this program:

function a(a){a()}