Add bundletool to DEPS and remove outdated header comment

[GaryQian]

Bundletool is needed to run integration tests for deferred components such as flutter/flutter#88030

Also removes the outdated header at the top of DEPS.

[rmistry]

Rollers into flutter engine (skia, dart, flutter sdk) are failing while running the license scripts after this change.

Logs:

I0817 13:06:18.259680      14 state_machine.go:838] Attempting to perform transition from "idle" to "active": upload roll
I0817 13:06:19.471315      14 deps_local.go:66] Running: python /data/depot_tools/gclient.py sync --delete_unversioned_trees --force
I0817 13:06:33.001540      14 deps_local.go:138] Running 1 pre-upload steps.
I0817 13:06:33.001575      14 pre_upload_steps.go:188] Running flutter license scripts.
I0817 13:06:33.001588      14 pre_upload_steps.go:194] Running put get.
I0817 13:06:33.452960      14 pre_upload_steps.go:209] Running [/data/src/third_party/dart/tools/sdks/dart-sdk/bin/dart lib/main.dart --src ../../.. --out /data/src/out/licenses --golden /data/src/flutter/ci/licenses_golden]
I0817 13:06:33.453023      14 exec.go:212] Executing '/data/src/third_party/dart/tools/sdks/dart-sdk/bin/dart lib/main.dart --src ../../.. --out /data/src/out/licenses --golden /data/src/flutter/ci/licenses_golden' (where /data/src/third_party/dart/tools/sdks/dart-sdk/bin/dart is /data/src/third_party/dart/tools/sdks/dart-sdk/bin/dart) with CWD /data/src/flutter/tools/licenses
lib/main.dart: Warning: Interpreting this as package URI, 'package:licenses/main.dart'.
Finding files...
../../../third_party/bundletool/.DS_Store
failed to handle ../../../third_party/bundletool/.DS_Store: FormatException: Unexpected extension byte (at offset 23)
failure: FormatException: Unexpected extension byte (at offset 23)
#0      _Utf8Decoder.convertSingle (dart:convert-patch/convert_patch.dart:1788:7)
#1      Utf8Decoder.convert (dart:convert/utf.dart:318:42)
#2      Utf8Codec.decode (dart:convert/utf.dart:63:20)
#3      UTF8TextFile.readString.<anonymous closure> (package:licenses/filesystem.dart:326:45)
#4      cache (package:licenses/cache.dart:15:20)
#5      UTF8TextFile.readString (package:licenses/filesystem.dart:326:14)
#6      _RepositoryApache4DNoticeFile.consider (package:licenses/main.dart:202:15)
#7      _RepositoryDirectory.createFile (package:licenses/main.dart:947:41)
#8      _RepositoryDirectory.crawl (package:licenses/main.dart:882:43)
#9      new _RepositoryDirectory (package:licenses/main.dart:856:5)
#10     new _RepositoryBundletoolDirectory (package:licenses/main.dart:1501:82)
#11     _RepositoryRootThirdPartyDirectory.createSubdirectory (package:licenses/main.dart:1872:14)
#12     _RepositoryDirectory.crawl (package:licenses/main.dart:877:46)
#13     new _RepositoryDirectory (package:licenses/main.dart:856:5)
#14     new _RepositoryGenericThirdPartyDirectory (package:licenses/main.dart:1242:89)
#15     new _RepositoryRootThirdPartyDirectory (package:licenses/main.dart:1811:86)
#16     _EngineSrcDirectory.createSubdirectory (package:licenses/main.dart:2376:14)
#17     _RepositoryDirectory.crawl (package:licenses/main.dart:877:46)
#18     new _RepositoryDirectory (package:licenses/main.dart:856:5)
#19     new _EngineSrcDirectory (package:licenses/main.dart:2346:42)
#20     main (package:licenses/main.dart:2625:39)
#21     _delayEntrypointInvocation.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:281:32)
#22     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:184:12)

aborted.

FYI @dnfield @zanderso