configure: Detect native NetBSD curses(3)

configure: Detect native NetBSD curses(3)

NetBSD ships with traditional BSD curses with compatibility with ncurses.
qemu works nicely with the basesystem version of curses(3) from NetBSD.

The only mismatch between curses(3) and ncurses is the lack of
curses_version() in the NetBSD version. This function is used solely in
the configure script, therefore eliminate it from the curses(3) detection.

With this change applied, configure detects correctly curses frontend.

Signed-off-by: Kamil Rytarowski <n54@gmx.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>