docs: fix typos and a stale API reference in lib comments - #7512

Three comment defects in lib/, each checked against the code it describes.

• lib/request.js (req.ip JSDoc): The is the remote address on the socket unless → This is the remote address on the socket unless. As written the sentence does not parse.
• lib/response.js (res.download): // support optional filename, where options may be in it's place → in its place. it's is the contraction, its the possessive.
• lib/response.js (res.format JSDoc): the comment says the method uses req.accepted, "an array of acceptable types ordered by their quality values". req.accepted was removed in Express 4 — History.md lists it under removed APIs ("req.accepted* - use req.accepts*() instead") — and the implementation calls req.accepts(keys) and uses the single best match it returns. Corrected to name the call that is actually made.

Comment text only: every changed line sits inside a comment and no code line is touched, so behaviour is unchanged.

A fourth instance of the same class, lib/application.js: "Render the given view name name with options", is left alone because #7388 already fixes that exact line.

Diff is 2 files and 3 comment fixes — small, clean, and non-controversial.