Deleting readonly class members does not give type error

[pablobirukov]

As @mhegazy said in #6717 deleting of readonly properties should follow the same rules as writing.

TypeScript Version: 2.0.3

Code

class Foo {
    public readonly bar: Bar;
    constructor() {
        this.bar = createBar(...);
    }
    public destroy() {
        delete this.bar; // here
    }
}

Expected behavior:
tsc should give a compile-time error
Actual behavior:
No error

[pablobirukov]

Associated with #11480

[RyanCavanaugh]

Any change we do in #11480 would apply equally here, so we can track the change at that issue. Thanks!