Several benchmarks started failing during kernel compile: 1. Timeouts: * commands_test * hot_mode_dev_cycle__benchmark * run_machine_concurrent_hot_reload * service_extensions_test 2. Kernel compiler crash: * hot_mode_dev_cycle_linux__benchmark * routing_test 3. Unexpected termination: * hot_mode_dev_cycle_win__benchmark This reverts commit ed63e7082ac89ea9851ae645ae69842da0c6150c.
Eliminates support for Dart 1 in flutter_tools, and drops our Dart 1 benchmarks. All commands now run in Dart 1 mode only. Eliminates --preview-dart-2 / --no-preview-dart-2 support.