Rename builder esprima fixtures to babel

f724ae98a1 changed the build
script to use Babel, so this commit updates the file names accordingly

external/builder/fixtures_babel/deadcode-expected.js

@@ -0,0 +1,21 @@
+function f1() {}
+function f2() {
+  return 1;
+}
+function f3() {
+  var i = 0;
+  throw "test";
+}
+function f4() {
+  var i = 0;
+}
+var obj = {
+  method1() {},
+  method2() {}
+};
+class C {
+  method1() {}
+  method2() {}
+}
+var arrow1 = () => {};
+var arrow2 = () => {};