Omit unused arg EXPECTED from socket hooks.

Omit unused arg EXPECTED from socket hooks.

* keyboard.c (gobble_input, read_avail_input, tty_read_avail_input):
* nsterm.m (ns_term_init):
* termhooks.h (struct terminal.read_socket_hook):
* w32inevt.c (w32_console_read_socket):
* w32term.c (w32_read_socket):
* xterm.c (XTread_socket):
Omit unused arg EXPECTED.  All callers changed.
(store_user_signal_events): Return void, not int, since callers no
longer care about the return value.  All uses changed.