cache-url: Remove TextEncoder

see #132

TextEncoder is not supported on some browsers, thus it would be good to remove this and use something else.

cc @sebastianbenz @kristoferbaxter

Start with issue #132 and locate the cache-url implementation that uses TextEncoder. Review the browser compatibility concern and identify the existing tests or entry point for cache-url; done means the unsupported API is no longer required and the affected behavior remains covered.

Written by the indexing model from the issue text.