[signatures] Component mismatch in examples

[tyler-ham]

There are a few places where the discussion text is out of sync with the examples.

• Section 2.3, reorder component names to match the example that follows:
  "The covered components consist of the @method, @path, and @authority
@authority, and @path derived component identifiers..."
• Section 3.2, reorder and update list of component names to match the example:
  "...that at least the method, path, authority, and cache-control authority,
  path, content-digest, content-length, and content-type be signed..."
• Section 5.1, remove the created parameter from the example. The surrounding discussion text makes it clear that created MUST NOT be included in the Accept-Signature field.