serial: use TERM=vt100 instead of TERM=vt100-nav

TERM=vt100-nav was necessary for compat with some ppc hvc devices, a
long time ago. Unfortunately vt100-nav terminfo is not installed by
default on most distros, hence change the default to v100 which is
available universally and still should be a relatively safe and
conservative default.

Should it turn out that vt100 is not really the best choice we can
revert this change again and then ask distros to move vt100-nav into
their default install.

src/util.c

@@ -3521,7 +3521,7 @@ const char *default_term_for_tty(const char *tty) {
 
         /* FIXME: Proper handling of /dev/console would be cool */
 
-        return "TERM=vt100-nav";
+        return "TERM=vt100";
 }
 
 static const char *const ioprio_class_table[] = {

units/serial-getty@.service.m4

@@ -22,7 +22,7 @@ After=rc-local.service
 Before=getty.target
 
 [Service]
-Environment=TERM=vt100-nav
+Environment=TERM=vt100
 m4_ifdef(`TARGET_FEDORA',
 ExecStartPre=-/sbin/securetty %I
 )m4_dnl