Revert "[#1164] move `web_components` line to dev_dependencies in the pu...

...bspec.yaml"

This reverts commit 51ee50a7d0691f8402196c74be368077606be93a.

I think [the discussion is not closed](https://github.com/angular/angular.dart/pull/1321#issuecomment-52259021) on this topic, easier to discuss here than on a closed PR.

@jbdeboer @vsavkin