Remove automatic adding @polymer/polymer package.json dependency

[platosha]

If my views are based on lit-element, I no longer need Polymer dependency in the project. But whenever I try to remove it, it is added back.

Steps reproduce:

• in a Flow app package.json, replace @polymer/polymer dependency with lit-element
• start the application

Expected: no changes in package.json

Actual: package.json is changed so that @polymer/polymer dependency is added back.

[haijian-vaadin]

Could it be that some view has some Vaadin components or Polymer components that are depending on @polymer/polymer?