Fix duplicated assertThisInitialized calls in constructors

[rubennorte]

Q	A
Fixed Issues?	Fixes #8335
Patch: Bug Fix?	Yes
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

This removes duplicated (and redundant) calls to the assertThisInitialized helper in constructors for subclasses in loose mode.

I've moved the detection of this to a later point in the transformation of the class to find the ones that are also added by super. calls, and then replaced them all at the same place (removing the redundancy in some cases).

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/9997/

[nicolo-ribaudo]

LGTM! While testing this PR, I found another bug:

class Bar {}

class Foo extends Bar {
  constructor() {
    0 && super();
    1 || super();
  }
}

new Foo // It should throw, but doesn't.

After that this PR is merged, would you like to fix it?

(This bug isn't introduced by your PR, it was already there).

[nicolo-ribaudo]

Thank you!