[dart2wasm] Don't assign offsets to selectors for dynamic calls
[dart2wasm] Don't assign offsets to selectors for dynamic calls

With a06f10c we started to generate direct calls in dynamic invocations
so we no longer need dispatch table entries for members that are only
invoked in dynamic invocations.

Change-Id: I29efd7f1486126c91f4286c84878b16db9c36a05
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/271880
Reviewed-by: Aske Simon Christensen <589eb3fd9a84f06d0ac46d3aa71dddcfb0814ccd@google.com>
Commit-Queue: Ömer Ağacan <d15e39adaef0c3a64e4ea5d68f5c1b5be1f04e29@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk