Update polymer-bundler's npm package files to eliminate test baggage

[usergenic]

Ran a diff of npm pack output and here is a summary of the changes.

• Before: 107 files, 607.9 kB
• After: 62 files, 345.5 kB

List of files no longer npm published after this update:

lib/test/bundle-manifest_test.d.ts
lib/test/bundle-manifest_test.js
lib/test/bundle-manifest_test.js.map
lib/test/bundler_test.d.ts
lib/test/bundler_test.js
lib/test/bundler_test.js.map
lib/test/constants_test.d.ts
lib/test/constants_test.js
lib/test/constants_test.js.map
lib/test/deps-index_test.d.ts
lib/test/deps-index_test.js
lib/test/deps-index_test.js.map
lib/test/es6-module-bundler_test.d.ts
lib/test/es6-module-bundler_test.js
lib/test/es6-module-bundler_test.js.map
lib/test/es6-module-bundling-scenarios_test.d.ts
lib/test/es6-module-bundling-scenarios_test.js
lib/test/es6-module-bundling-scenarios_test.js.map
lib/test/html-bundler_test.d.ts
lib/test/html-bundler_test.js
lib/test/html-bundler_test.js.map
lib/test/import-meta-url_test.d.ts
lib/test/import-meta-url_test.js
lib/test/import-meta-url_test.js.map
lib/test/parse5-utils_test.d.ts
lib/test/parse5-utils_test.js
lib/test/parse5-utils_test.js.map
lib/test/polymer-bundler_test.d.ts
lib/test/polymer-bundler_test.js
lib/test/polymer-bundler_test.js.map
lib/test/shards_test.d.ts
lib/test/shards_test.js
lib/test/shards_test.js.map
lib/test/sourcemap_test.d.ts
lib/test/sourcemap_test.js
lib/test/sourcemap_test.js.map
lib/test/test-utils_test.d.ts
lib/test/test-utils_test.js
lib/test/test-utils_test.js.map
lib/test/test-utils.d.ts
lib/test/test-utils.js
lib/test/test-utils.js.map
lib/test/url-utils_test.d.ts
lib/test/url-utils_test.js
lib/test/url-utils_test.js.map

[justinfagnani]

See #829 (comment)