[trivial patch] remove superflous #ifdef

[Crystal Kolipe]

The KASSERT macro is a NOP unless DIAGNOSTIC is defined, so it doesn't need to
be in an #ifdef here:

--- dev/wscons/wsemul_vt100.c.dist      Mon May 25 06:55:49 2020
+++ dev/wscons/wsemul_vt100.c   Sat Dec 31 20:37:14 2022
@@ -204,9 +204,7 @@
 
        if (console) {
                edp = &wsemul_vt100_console_emuldata;
-#ifdef DIAGNOSTIC
                KASSERT(edp->console == 1);
-#endif
        } else {
                edp = malloc(sizeof *edp, M_DEVBUF, M_NOWAIT);
                if (edp == NULL)