unnecessary_dev_dependency

The dev dependency on {0} is unnecessary because there is also a normal dependency on that package.

The analyzer produces this diagnostic when there's an entry under dev_dependencies for a package that is also listed under dependencies. The packages under dependencies are available to all of the code in the package, so there's no need to also list them under dev_dependencies.

The following code produces this diagnostic because the package meta is listed under both dependencies and dev_dependencies:

name: example
dependencies:
  meta: ^1.0.2
dev_dependencies:
  meta: ^1.0.2

Remove the entry under dev_dependencies (and the dev_dependencies key if that's the only package listed there):

name: example
dependencies:
  meta: ^1.0.2