[gn] Remove dart_test_bootfs

This doesn't look like it could have been working for a while.
It uses obsolete Fuchsia GN infrastructure that is going away.
If a test setup like this is useful it can be resurrected in a
new form that fits into the current Fuchsia ways of doing things.

Change-Id: I41e2ad5948cbf71a5e83f8e2f3235aa0dbd5c9a3
Reviewed-on: https://dart-review.googlesource.com/64022
Reviewed-by: Zach Anderson <zra@google.com>
Commit-Queue: Zach Anderson <zra@google.com>

BUILD.gn

@@ -151,46 +151,3 @@ group("compressed_observatory_archive") {
     "runtime/observatory:copy_compressed_observatory_archive",
   ]
 }
-
-# The rules below build a Fuchsia OS image that includes the Dart tree
-# under /system/test/dart.  To get this into the `user.bootfs` generated
-# by the Fuchsia build, add the GN build argument:
-#   extra_bootdata = [ "//third_party/dart:dart_test_bootfs" ]
-if (is_fuchsia) {
-  import("//build/config/fuchsia/bootdata.gni")
-
-  action("generate_dart_test_manifest") {
-    testonly = true
-
-    output_prefix = "$target_gen_dir/dart_test_tree"
-    outputs = [
-      "$output_prefix.manifest",
-    ]
-
-    mode = "release"
-    if (is_debug) {
-      mode = "debug"
-    }
-
-    script = "tools/gen_fuchsia_test_manifest.py"
-    args = [
-      "-m",
-      mode,
-      "-o",
-      rebase_path(output_prefix),
-    ]
-  }
-
-  bootdata("dart_test_bootfs") {
-    testonly = true
-    deps = [
-      ":generate_dart_test_manifest",
-      "runtime/bin:dart",
-      "runtime/bin:process_test",
-      "runtime/bin:run_vm_tests",
-    ]
-    inputs = [
-      "$target_gen_dir/dart_test_tree.manifest",
-    ]
-  }
-}