Use CSSselect library directly

The "cheerio-select" library does not offer additional functionality,
seeming to serve as a simple wrapper around the "CSSselect" library. Its
inclusion in Cheerio it makes the project:

- More difficult to understand (contributors must read through that
  library's source before recognizing CSS selector bugs originate from
  CSSselect)
- Less efficient (it introduces an additional function call and
  processing overhead)
- More difficult to maintain (CSSselect releases must first be approved
  by "cheerio-select" before they can reach Cheerio itself)