Make sure iron-lazy-pages does not generate linter errors

[TimvdLippe]

Apparently the correct 2.0 version of iron-lazy-pages generates linter errors of polymer lint. This should not be happening. Not sure when I have time to investigate and address the issues.

• Lazy imports are generating warnings, as the analyzer is not traversing the lazy imports of iron-lazy-pages.
  • A PR is open to support this in the polymer-analyzer (Add support for lazy-imports of iron-lazy-pages Polymer/polymer-analyzer#600), but I do not think that one will be merged.
  • There is a behavior (https://github.com/Polymer/lazy-imports) that would resolve the linter errors, but forces more source code changes for the 2.0 version + import another behavior.
  • Maybe the behavior is not required and the user only needs to specify the rel="lazy-import", without actually any source code changes to iron-lazy-pages.