Revert "[ DartDev ] Generate dartdev.dart.snapshot for runtime builds and place it in the root of the build output directory"

This reverts commit 367ee916d6.

Reason for revert: Build failures

Original change's description:
> [ DartDev ] Generate dartdev.dart.snapshot for runtime builds and place it in the root of the build output directory
> 
> VM developers rarely run the create_sdk build as it's significantly
> slower than just building the VM. Since DartDev is coupled to the VM, we
> should build it to ensure that there's no snapshot errors due to old
> snapshots from previous create_sdk builds.
> 
> Change-Id: I7626e0f3c791f2a6e69830641d9abf043ec5138f
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/144465
> Reviewed-by: Jaime Wren <jwren@google.com>
> Commit-Queue: Ben Konyi <bkonyi@google.com>

TBR=jwren@google.com,bkonyi@google.com,asiva@google.com

Change-Id: I36754f7830e637313a390218d16869a8528f75ff
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/144622
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>

utils/dartdev/BUILD.gn

@@ -18,15 +18,8 @@ dartfix_files = exec_script("../../tools/list_dart_files.py",
                             ],
                             "list lines")
 
-copy("dartdev") {
-  deps = [ ":dartdev_snapshot" ]
-  sources = [ "$root_gen_dir/dartdev.dart.snapshot" ]
-  outputs = [ "$root_out_dir/dartdev.dart.snapshot" ]
-}
-
-application_snapshot("dartdev_snapshot") {
+application_snapshot("dartdev") {
   main_dart = "../../pkg/dartdev/bin/dartdev.dart"
   training_args = [ "--help" ]
   inputs = dartdev_files + dartfix_files
-  output = "$root_gen_dir/dartdev.dart.snapshot"
 }