Revert "Create the frontend_server snapshot as a part of the sdk"

This reverts commit 24a0601.

Reason for revert: This breaks the flutter build because flutter has
a build target producing the same "gen/frontend_server.dart.snapshot" file and is therefore conflicting.

See e.g. head-head-head bot failure:

    https://ci.chromium.org/p/dart/builders/ci.sandbox/flutter-engine-linux/9747


Original change's description:
> Create the frontend_server snapshot as a part of the sdk
> 
> This will allow us to use it from webdev, as it now supports DDC output.
> 
> Change-Id: I4b82d1c45d2c058abb062dddd2a2c41cc6318c45
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/130134
> Reviewed-by: Keerti Parthasarathy <keertip@google.com>
> Reviewed-by: Jonah Williams <jonahwilliams@google.com>
> Reviewed-by: Vijay Menon <vsm@google.com>
> Commit-Queue: Jake Macdonald <jakemac@google.com>

TBR=keertip@google.com,jakemac@google.com,vsm@google.com,jonahwilliams@google.com

Change-Id: Ib2d782560cc005416ece429f9506dca055bffd9b
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/130377
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>

sdk/BUILD.gn

@@ -182,10 +182,6 @@ _full_sdk_snapshots = [
     "pub",
     "../utils/pub",
   ],
-  [
-    "frontend_server",
-    "../utils/kernel-service:frontend_server",
-  ],
 ]
 if (include_dart2native && dart_target_arch != "ia32") {
   _full_sdk_snapshots += [ [

sdk_nnbd/BUILD.gn

@@ -182,10 +182,6 @@ _full_sdk_snapshots = [
     "pub",
     "../utils/pub",
   ],
-  [
-    "frontend_server",
-    "../utils/kernel-service:frontend_server",
-  ],
 ]
 if (include_dart2native && dart_target_arch != "ia32") {
   _full_sdk_snapshots += [ [

utils/kernel-service/BUILD.gn

@@ -59,19 +59,7 @@ application_snapshot("frontend_server") {
     "--platform=$sdk_root/vm_platform_strong.dill",
     rebase_path(main_dart),
   ]
-  output = "$root_gen_dir/frontend_server.dart.snapshot"
-}
-
-copy("copy_frontend_server") {
-  deps = [
-    ":frontend_server",
-  ]
-  sources = [
-    "$root_gen_dir/frontend_server.dart.snapshot",
-  ]
-  outputs = [
-    "$root_out_dir/frontend_server.dart.snapshot",
-  ]
+  output = "$root_out_dir/frontend_server.dart.snapshot"
 }
 
 template("kernel_service_dill") {