[VM] Remove support for option --no-preview-dart-2

- option --no-preview-dart-2 will now result in an error
- change aot-assembly build rule to generate AOT snapshot using Dart 2
- generate coresnapshot using Dart 2 (this snapshot is not used yet, next CL which switch the isolate create code to use this snapshot)
- by pass all Dart1 test runs in the status file
- change the default compiler setting in test.py to use dartk
- have test.py not pick up any configuration for --no-preview-dart-2

Change-Id: Ia136943ebfd0fed0c52683b330745b3e2c7a7ce6
Reviewed-on: https://dart-review.googlesource.com/75820
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Siva Annamalai <asiva@google.com>

utils/application_snapshot.gni

@@ -216,18 +216,13 @@ template("aot_assembly") {
       output,
     ]
 
-    abs_depfile = rebase_path(depfile)
     abs_output = rebase_path(output, root_build_dir)
 
     vm_args = [
-      # TODO(asiva): For not use --no-preview-dart-2, need to flip this to use
-      # gen_kernel to generate a kernel file before creating an app snapshot.
-      "--no-preview-dart-2",
       "--deterministic",
       "--packages=$dot_packages",
       "--snapshot-kind=app-aot",
       "--snapshot=$abs_output",
-      "--snapshot-depfile=$abs_depfile",
     ] + aot_vm_args
 
     args = []