Remove the tests step and the following steps from the mac tests for web

Tests run on led: https://chromium-swarm.appspot.com/task?id=4c7b95dd7c98d010



Change-Id: I9483477463959a30e0d702c8c8ea41c7d34f11a3
Reviewed-on: https://flutter-review.googlesource.com/c/recipes/+/3162
Reviewed-by: Godofredo Contreras <godofredoc@google.com>
Reviewed-by: Christopher Fujino <fujino@google.com>