Delete polymer from the Dart repo

pkg/polymer/pubspec.yaml

-name: polymer
-version: 0.15.3+1
-author: Polymer.dart Authors <web-ui-dev@dartlang.org>
-description: >
-  Polymer.dart is a new type of library for the web, built on top of Web
-  Components, and designed to leverage the evolving web platform on modern
-  browsers.
-homepage: https://www.dartlang.org/polymer-dart/
-dependencies:
-  analyzer: '>=0.15.6 <0.23.0'
-  args: '>=0.11.0 <0.13.0'
-  barback: '>=0.14.2 <0.16.0'
-  browser: '>=0.10.0 <0.11.0'
-  code_transformers: '>=0.2.3 <0.3.0'
-  html5lib: '>=0.12.0 <0.13.0'
-  logging: '>=0.9.2 <0.10.0'
-  path: '>=0.9.0 <2.0.0'
-  polymer_expressions: '>=0.12.0 <0.14.0'
-  smoke: '>=0.2.0 <0.3.0'
-  source_maps: '>=0.9.4 <0.11.0'
-  source_span: '>=1.0.0 <2.0.0'
-  template_binding: '>=0.12.0 <0.15.0'
-  web_components: '>=0.10.0 <0.11.0'
-  yaml: '>=0.9.0 <3.0.0'
-
-  # Because polymer exports observe, it needs to keep its version constraint
-  # tight to ensure that a constraint on polymer properly constraints all
-  # features it provides.
-  observe: '>=0.12.2 <0.12.3'
-dev_dependencies:
-  unittest: '>=0.10.0 <0.12.0'
-  markdown: '>=0.7.0 <0.8.0'
-transformers:
-- polymer/src/build/mirrors_remover:
-    $include: lib/polymer.dart
-- code_transformers/src/delete_file:
-    $include:
-      - lib/src/build/log_injector.css
-      - lib/src/js/polymer/polymer.js
-- observe:
-    files: lib/src/instance.dart
-    $include: lib/src/instance.dart
-environment:
-  sdk: '>=1.4.0 <2.0.0'