Remove support for old parameter syntax/runtime behavior

[DartBot]

This issue was originally filed by ngeoffray@google.com

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After issue #5073 has been fixed and we upgrade all code base to the new syntax.

[kasperl]

Removed this from the M1 milestone.
Added this to the M2 milestone.

[kasperl]

Removed this from the M2 milestone.

[kasperl]

Added this to the M2 milestone.

[kasperl]

Removed Priority-Medium label.
Added Priority-High label.

[kasperl]

Fixed by Regis in r13891. The value for the REJECT_NAMED_ARGUMENT_AS_POSITIONAL flag in compiler.dart is now true.

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Added Fixed label.