Remove ifdef BOOTCDROM option to start init.

When BOOTCDROM is defined (via CFLAGS as there is no config option)
it causes -C to be passed to init, but our init and the version of
sysinstall I glanced at in 6.x don't support -C. The last plausibly
related support was removed from the tree in 1995.

Reviewed by:	kib
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D18431

sys/kern/init_main.c

@@ -774,10 +774,6 @@ start_init(void *dummy)
 			*flagp++ = 'f';
 			options++;
 		}
-#endif
-#ifdef BOOTCDROM
-		*flagp++ = 'C';
-		options++;
 #endif
 		if (options == 0)
 			*flagp++ = '-';