[SDK] Cleans up a few unused functions in core_types.dart.
[SDK] Cleans up a few unused functions in core_types.dart.

Change-Id: I5fc97b26f194434e70c814ba78ae6d17f97f4fbf
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127145
Reviewed-by: Dmitry Stefantsov <95a4b7e39916a54bd6477bec6a6de014b977db32@google.com>
Commit-Queue: Clement Skau <495593248b6158163719b90dde8357b589c8e5d0@google.com>

dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk