Disable (comment out) options DIAGNOSTIC in INSTALL kernels.

It has been there since the initial revision 1.1 while
it was disabled in GENERIC in revision 1.121 back in 2002:
 http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/arch/mac68k/conf/GENERIC#rev1.121

Briefly discussed in PR/57107, and maybe should be pulled up to
netbsd-9 and netbsd-10.

sys/arch/mac68k/conf/INSTALL

@@ -1,4 +1,4 @@
-#	$NetBSD: INSTALL,v 1.57 2020/08/10 06:32:58 rin Exp $
+#	$NetBSD: INSTALL,v 1.58 2023/01/05 18:48:13 tsutsui Exp $
 #
 # INSTALL
 
@@ -38,7 +38,7 @@ options		PIPE_SOCKETPAIR		# smaller, but slower pipe(2)
 #options 	SYSCTL_INCLUDE_DESCR	# Include sysctl descriptions in kernel
 
 # Diagnostic/debugging support options - XXX remove these at some point
-options 	DIAGNOSTIC	# cheap kernel consistency checks
+#options 	DIAGNOSTIC	# cheap kernel consistency checks
 options 	DDB		# in-kernel debugger
 pseudo-device	ksyms
 #options 	ADB_DEBUG	# ADB debugging