gh-150952: Fix incorrect sock_sendto docstring (#150953)

Author: deadlovelll

Lib/asyncio/selector_events.py

@@ -586,14 +586,10 @@ def _sock_sendall(self, fut, sock, view, pos):
             pos[0] = start
 
     async def sock_sendto(self, sock, data, address):
-        """Send data to the socket.
+        """Send a datagram from sock to address.
 
-        The socket must be connected to a remote socket.  This method
-        continues to send data from data until either all data has been
-        sent or an error occurs.  None is returned on success.  On error,
-        an exception is raised, and there is no way to determine how much
-        data, if any, was successfully processed by the receiving end of
-        the connection.
+        The socket does not have to be connected. This method sends the
+        whole datagram in a single call. Return the number of bytes sent.
         """
         base_events._check_ssl_socket(sock)
         if self._debug and sock.gettimeout() != 0: