Minor cleanup for terminal setup.

Minor cleanup for terminal setup.
* termhooks.h (create_terminal): Adjust prototype.
* terminal.c (create_terminal): Pass output method and RIF as args.
(init_initial_terminal):
* nsterm.m (ns_create_terminal):
* term.c (init_tty):
* w32term.c (w32_create_terminal):
* xterm.c (x_create_terminal): Adjust users.
Avoid redundant NULL initializers and add comments.