The principle is the same as in `PoolManager._new_pool()`, where I borrowed the code from: some keyword arguments apply only to `HTTPSConnectionPool`s, but we don't want the caller to have to deal with not passing those extra arguments if the URL scheme is `http`, rather than `https`. So we let them pass all the arguments, and remove the SSL-related ones if they don't apply.

Would you like me to change it? I suppose a marginal improvement would be to group the SSL-related arguments into some kind of `SSLParams` class, so they don't have to be repeated in a bunch of places (`HTTPSConnection`, `VerifiedHTTPSConnection`, `HTTPSConnectionPool`, `ssl_wrap_socket`), but that may be outside the scope of this PR.