[build] Collapse now-identical application_snapshot and kernel_application_snapshot.

Change-Id: I6aabe13b9e4adcfcfb073197e9b6b5605e16e30c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/310968
Reviewed-by: Alexander Aprelev <aam@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

Author: rmacnak-google

utils/application_snapshot.gni

@@ -45,7 +45,7 @@ declare_args() {
 #
 #  output (optional):
 #    Overrides the full output path.
-template("_application_snapshot") {
+template("application_snapshot") {
   assert(defined(invoker.main_dart), "Must specify 'main_dart'")
   assert(defined(invoker.training_args), "Must specify 'training_args'")
   if (defined(invoker.dart_snapshot_kind)) {
@@ -184,68 +184,3 @@ template("_application_snapshot") {
     }
   }
 }
-
-# Creates an app-jit snapshot for a Dart2 program based on a training run.
-#
-# Parameters:
-#  main_dart (required):
-#    The entrypoint to the Dart application.
-#
-#  training_args (required):
-#    Arguments to pass to the Dart application for the training run.
-#
-#  vm_args (optional):
-#    Additional arguments to the Dart VM.
-#
-#  name (optional):
-#    The name of the snapshot if different from the target name. The output
-#    will be in $root_gen_dir/$name.dart.snapshot.
-#
-#  deps (optional):
-#    Any build dependencies.
-#
-#  dot_packages (optional):
-#    The package config file for the app. Defaults to
-#    $_dart_root/.dart_tool/package_config.json.
-#
-#  output (optional):
-#    Overrides the full output path.
-template("application_snapshot") {
-  _application_snapshot(target_name) {
-    forward_variables_from(invoker, "*")
-    if (!defined(invoker.deps)) {
-      deps = []
-    }
-  }
-}
-
-# Creates an app-jit snapshot for the common FE based on a training run.
-#
-# Parameters:
-#  main_dart (required):
-#    The entrypoint to the Dart application.
-#
-#  training_args (required):
-#    Arguments to pass to the Dart application for the training run.
-#
-#  vm_args (optional):
-#    Additional arguments to the Dart VM.
-#
-#  name (optional):
-#    The name of the snapshot if different from the target name. The output
-#    will be in $root_gen_dir/$name.dart.snapshot.
-#
-#  deps (optional):
-#    Any build dependencies.
-#
-#  dot_packages (optional):
-#    The packages config file for the app. Defaults to
-#    $_dart_root/.dart_tool/package_config.json.
-#
-#  output (optional):
-#    Overrides the full output path.
-template("kernel_application_snapshot") {
-  _application_snapshot(target_name) {
-    forward_variables_from(invoker, "*")
-  }
-}

utils/kernel-service/BUILD.gn

@@ -16,7 +16,7 @@ group("kernel-service") {
   }
 }
 
-kernel_application_snapshot("kernel-service_snapshot") {
+application_snapshot("kernel-service_snapshot") {
   main_dart = "../../pkg/vm/bin/kernel_service.dart"
   training_args = [
     "--train",