LTS support
-LTS build model removes depot_tools recipe each change in FLUTTER_SDK_TAG requires running the scripts/gclient_bitbake.py to generate conf/include/flutter-engine_%.inc. LTS support requires minor change to conf/include/flutter-engine_%.inc for using Dart SDK prebuilt via http fetcher.
-Removal of depot_tools No longer required
Signed-off-by: Joel Winarske joel.winarske@gmail.com