VM: No compile-time error when a named constructor's id duplicates that of another member

[DartBot]

This issue was originally filed by [email protected]

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as resolution of issue #3040, spec now says:
A constructor name always begins with the name of its immediately enclosing class or interface, and may optionally be followed by a dot and an identifier id. It is a compile-time error if id is the name of a member declared in the immediately enclosing class.

However, the following co19 test executes without a hitch on VM r13643:
Language/07_Classes/6_Constructors_A01_t01

class C {
  var foo;
  C.foo();
}

main() {
  try {
    new C.foo();
  } catch (e){}
}

[dgrove]

Added Area-VM, Triaged labels.

[iposva-google]

Time to remove the legacy support.

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Set owner to @mhausner.
Added this to the M2 milestone.
Added Accepted label.

[DartBot]

This comment was originally written by @mhausner

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Enabled the existing check by default. Test now passes.

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Added Fixed label.