Do not transpile typeof helper with itself in babel/runtime

[nicolo-ribaudo]

Q	A
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

I noticed that the typeof.js helper also contained a copy of itself as _typeof2: https://unpkg.com/browse/@babel/runtime@7.7.4/helpers/typeof.js
This PR removes it:

function _typeof(obj) {
  if (typeof Symbol === "function" && typeof Symbol.iterator === "symbol") {
    module.exports = _typeof = function _typeof(obj) {
      return typeof obj;
    };
  } else {
    module.exports = _typeof = function _typeof(obj) {
      return obj && typeof Symbol === "function" && obj.constructor === Symbol && obj !== Symbol.prototype ? "symbol" : typeof obj;
    };
  }

  return _typeof(obj);
}

module.exports = _typeof;

In other helpers it is still transformed:

var _typeof = require("../helpers/typeof");

var toPrimitive = require("./toPrimitive");

function _toPropertyKey(arg) {
  var key = toPrimitive(arg, "string");
  return _typeof(key) === "symbol" ? key : String(key);
}

module.exports = _toPropertyKey;

[nicolo-ribaudo]

CircleCI is failing because of core-js 3.4.6. It's fixed in 3.4.7, but I don't know how to clear the cache before triggering a build.

[Andarist]

Could we exclude this plugin altogether and only allow using typeof helper as an explicit dependency of other helpers when needed? This probably cannot be done right now as the expectation is to ship es5-compatible code.

[nicolo-ribaudo]

I have a better alternative to this PR.

[nicolo-ribaudo]

Nevermind, it doesn't work. (I was trying to rewrite the helper so that it wouldn't be transformed by the typeof plugin)