curl_multi_socket.3: remove callback and typical usage descriptions

1. The callback is better described in the option for setting it. Having
it in a single place reduces the risk that one of them is wrong.

2. The "typical usage" is wrong since the functions described in this
man page are both deprecated so they cannot be used in any "typical" way
anymore.

Closes #8262

docs/libcurl/curl_multi_socket.3

@@ -5,7 +5,7 @@
 .\" *                            | (__| |_| |  _ <| |___
 .\" *                             \___|\___/|_| \_\_____|
 .\" *
-.\" * Copyright (C) 1998 - 2021, Daniel Stenberg, <daniel@haxx.se>, et al.
+.\" * Copyright (C) 1998 - 2022, Daniel Stenberg, <daniel@haxx.se>, et al.
 .\" *
 .\" * This software is licensed as described in the file COPYING, which
 .\" * you should have received as part of this distribution. The terms
@@ -66,68 +66,6 @@ equivalent to \fIcurl_multi_socket_action(3)\fP with \fBev_bitmask\fP set to
 Force libcurl to (re-)check all its internal sockets and transfers instead of
 just a single one by calling \fIcurl_multi_socket_all(3)\fP. Note that there
 should not be any reason to use this function.
-.SH CALLBACK
-The socket \fBcallback\fP function uses a prototype like this
-.nf
-  int curl_socket_callback(CURL *easy,      /* easy handle */
-                           curl_socket_t s, /* socket */
-                           int action,      /* see values below */
-                           void *userp,    /* private callback pointer */
-                           void *socketp); /* private socket pointer */
-.fi
-The callback MUST return 0.
-
-The \fIeasy\fP argument is a pointer to the easy handle that deals with this
-particular socket. Note that a single handle may work with several sockets
-simultaneously.
-
-The \fIs\fP argument is the actual socket value as you use it within your
-system.
-
-The \fIaction\fP argument to the callback has one of five values:
-.RS
-.IP "CURL_POLL_NONE (0)"
-register, not interested in readiness (yet)
-.IP "CURL_POLL_IN (1)"
-register, interested in read readiness
-.IP "CURL_POLL_OUT (2)"
-register, interested in write readiness
-.IP "CURL_POLL_INOUT (3)"
-register, interested in both read and write readiness
-.IP "CURL_POLL_REMOVE (4)"
-unregister
-.RE
-
-The \fIsocketp\fP argument is a private pointer you have previously set with
-\fIcurl_multi_assign(3)\fP to be associated with the \fIs\fP socket. If no
-pointer has been set, socketp will be NULL. This argument is of course a
-service to applications that want to keep certain data or structs that are
-strictly associated to the given socket.
-
-The \fIuserp\fP argument is a private pointer you have previously set with
-\fIcurl_multi_setopt(3)\fP and the \fICURLMOPT_SOCKETDATA(3)\fP option.
-.SH "TYPICAL USAGE"
-1. Create a multi handle
-
-2. Set the socket callback with \fICURLMOPT_SOCKETFUNCTION(3)\fP
-
-3. Set the timeout callback with \fICURLMOPT_TIMERFUNCTION(3)\fP, to get to
-know what timeout value to use when waiting for socket activities.
-
-4. Add easy handles with curl_multi_add_handle()
-
-5. Provide some means to manage the sockets libcurl is using, so you can check
-them for activity. This can be done through your application code, or by way
-of an external library such as libevent or glib.
-
-6. Wait for activity on any of libcurl's sockets, use the timeout value your
-callback has been told
-
-7, When activity is detected, call curl_multi_socket_action() for the
-socket(s) that got action. If no activity is detected and the timeout expires,
-call \fIcurl_multi_socket_action(3)\fP with \fICURL_SOCKET_TIMEOUT\fP
-
-8. Go back to step 6.
 .SH EXAMPLE
 .nf
 /* the event-library gets told when there activity on the socket 'fd',