cleanup https://github.com/flutter/flutter/issues/5789

It's safe to remove the unneeded `void`s from setters since the blocking issues in the
`always_declare_return_types` lint have been fixed (https://github.com/dart-lang/linter/).  We can also safely flip the bit on  `avoid_return_types_on_setters`.

* better parsing of adb devices output

* re-order lines

* fix analysis errors

* review comments; fix test

* re-add an export for debugPrint

And fix a zillion omissions this uncovered.

remove the device factory methods as well as the device cache

rename to printTrace(), printStatus(), and printError()