Remove the BSD/OS 2.1 system call gate LDT entry.

An extra copy of the system call gate was added to the default LDT back
in 1996 (r18513 / r18514).  However, the ability to run BSD/OS 2.1
i386 binaries under FreeBSD's native ABI is most likely no longer
needed.

Discussed with:	kib

sys/i386/i386/machdep.c

@@ -2446,10 +2446,6 @@ init386(int first)
 	gdp->gd_p = 1;
 	gdp->gd_hioffset = x >> 16;
 
-	/* XXX does this work? */
-	/* XXX yes! */
-	ldt[LBSDICALLS_SEL] = ldt[LSYS5CALLS_SEL];
-
 	/* transfer to user mode */
 
 	_ucodesel = GSEL(GUCODE_SEL, SEL_UPL);

sys/x86/include/segments.h

@@ -252,8 +252,7 @@ union descriptor {
 #define	LUDATA_SEL	5
 /* separate stack, es,fs,gs sels ? */
 /* #define	LPOSIXCALLS_SEL	5*/	/* notyet */
-#define	LBSDICALLS_SEL	16	/* BSDI system call gate */
-#define	NLDT		(LBSDICALLS_SEL + 1)
+#define	NLDT		(LUDATA_SEL + 1)
 
 #else /* !__i386__ */
 /*