Remove unused parts of strip-comments

[ojeytonwilliams]

          Going through this made it obvious just how little of strip-comments we actually use. 

We should expand our tests a little (since we're implicitly relying on a bunch of tests in https://github.com/jonschlinkert/strip-comments that we don't run) and remove everything we don't need, but I'll do that in another PR.

Originally posted by @ojeytonwilliams in #120 (comment)

[a2937]

Hi there. Should a test with this as the expected output actually pass? As things stand right now, I'm fairly certain it won't pass.

https://github.com/jonschlinkert/strip-comments/blob/master/test/expected/html/quoted.html