Kill termio.h and sys/termios.h

1. On FreeBSD, compilation complains that "this file includes <sys/termios.h> which is deprecated, use <termios.h> instead". On Linux and FreeBSD, <sys/termios.h> literally just pulls in <termios.h>. On OS X and Solaris, <termios.h> pulls in <sys/termios.h>.

2. <termio.h> doesn't exist on FreeBSD or Mac OS X, and on Linux is marked as deprecated and just includes <termios.h>. It does exist on Solaris, but no `struct termio` is ever actually used in the codebase.

(This will not merge with the changes in my kill-gettext branch as suggested for #548 but I will update one or the other if they get merged at different times)