Remove obsolete target sign_updater

Our devops code now contains this logic.

build/mac/BUILD.gn

@@ -640,41 +640,3 @@ crx3("crx") {
   key = "//brave/updater/crx-private-key.der"
   deps = [ ":copy_dmg_pkg" ]
 }
-
-action("sign_updater") {
-  deps = [
-    "//chrome/updater/mac:updater_bundle",
-    "//chrome/updater/mac:updater_install_script",
-    "//chrome/updater/mac/installer:metainstaller",
-    "//chrome/updater/mac/signing",
-    "//chrome/updater/tools:BraveUpdaterUtil",
-  ]
-  script = "sign_updater.py"
-  output_dir = "$root_out_dir/$mac_signed_output_prefix"
-  output_file = "$updater_product_full_name-$chrome_version_full.zip"
-  args = [
-    rebase_path("$root_out_dir/Updater Packaging/sign_updater.py",
-                root_build_dir),
-    rebase_path(output_dir),
-    output_file,
-    "--input",
-    rebase_path(root_out_dir),
-    "--identity",
-    mac_signing_identifier,
-    "--installer-identity",
-    mac_installer_signing_identifier,
-  ]
-  if (notarize) {
-    args += [
-      "--notarize",
-      "--notary-arg=--apple-id",
-      "--notary-arg=$notary_user",
-      "--notary-arg=--password",
-      "--notary-arg=$notary_password",
-      "--notary-arg=--team-id",
-      "--notary-arg=$chrome_mac_team_id",
-    ]
-  }
-  outputs = [ "$output_dir/$output_file" ]
-  inputs = [ script ]
-}