Revert "Show output from pub get in flutter pub get"

[zanderso]

Reverts #106300

This PR appears to have caused persistent timing out on Windows for the test here: https://ci.chromium.org/p/flutter/builders/prod/Windows_android%20windows_chrome_dev_mode

[zanderso]

Timing out on the step:

[windows_chrome_dev_mode] [STDOUT] Executing "C:\opt\s\w\ir\x\w\recipe_cleanup\tmp1ippl8tu\flutter sdk\bin\flutter packages get" in "C:\opt\s\w\ir\x\t\edited_flutter_gallery" with environment {BOT: true, LANG: en_US.UTF-8}

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Validations Fail.

[whesse]

The problem appears to be in the Flutter test that is timing out. It is running "dart pub get" in a subprocess using Dart's Process.start, but not listening on or draining stdout, so it is hanging if the pipe gets full.

https://github.com/flutter/flutter/blob/master/dev/devicelab/lib/tasks/web_dev_mode_tests.dart#L45