[build] Don't list Dart sources up front when creating application snapshots.

GN/Ninja will discover them via the depfile created alongside the snapshot.

Bug: https://github.com/flutter/flutter/issues/81074
Change-Id: I6e0f07214e8ea29e6d23261c71558da06fd2223a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196982
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Ryan Macnak <rmacnak@google.com>

utils/dartdev/BUILD.gn

@@ -4,13 +4,6 @@
 
 import("../application_snapshot.gni")
 
-dartdev_files = exec_script("../../tools/list_dart_files.py",
-                            [
-                              "absolute",
-                              rebase_path("../../pkg/dartdev"),
-                            ],
-                            "list lines")
-
 group("dartdev") {
   public_deps = [
     ":copy_dartdev_kernel",
@@ -30,7 +23,6 @@ application_snapshot("generate_dartdev_kernel") {
   main_dart = "../../pkg/dartdev/bin/dartdev.dart"
   training_args = []
   deps = [ "../dds:dds" ]
-  inputs = dartdev_files
   output = "$root_gen_dir/dartdev.dill"
 }
 
@@ -45,6 +37,5 @@ application_snapshot("generate_dartdev_snapshot") {
   main_dart = "../../pkg/dartdev/bin/dartdev.dart"
   training_args = [ "--help" ]
   deps = [ "../dds:dds" ]
-  inputs = dartdev_files
   output = "$root_gen_dir/dartdev.dart.snapshot"
 }