wsvt25 backspace key should match terminfo definition

[RVP <rvp%SDF.ORG@localhost>]

The kernel currently defines the backspace key as:

$ fgrep CERASE /usr/include/sys/ttydefaults.h
#define CERASE          0177
$

This should probably be changed to CTRL('h') to match both the
NetBSD and GNU terminfo backspace key definitions, otherwise
the key doesn't work right after reset(1) or tset(1):

$ infocmp wsvt25 | tr ',' '\n' | fgrep kbs
# Reconstructed from /usr/share/misc/terminfo.cdb
wsvt25|NetBSD wscons in 25 line DEC VT220 mode,
[...]
 kbs=^H

$ /opt/ncurses/bin/infocmp wsvt25 | tr ',' '\n' | fgrep kbs
#       Reconstructed via infocmp from file: /opt/ncurses/share/terminfo/w/wsvt25
wsvt25|NetBSD wscons in 25 line DEC VT220 mode,
[...]
 kbs=^H
$

Thanks,
-RVP