tty/pty: change back default CERASE to ^H
tty/pty: change back default CERASE to ^H

Alternatives should be considered (such as changing our keymaps to
better match NetBSD) in due time, but for now, the current default
is incredibly annoying!

Change-Id: I4cab5d6a9f39983ee8aa80362768fdb9cf3db948

veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi,veritas-shine/minix3-rpi