Remove UNSAFE flag. (#134)

This flag was for SunOS 3 and 4 on sun3 hardware (68k).

It enabled some unsafe optimizations via assembler. This hasn't
actually been built since the DOS port (since the header for this
was renamed, but the code in `xc.c` wasn't updated).

The optimizations here made assumptions that were specific to the
68k hardware and register allocation. They aren't likely to be
of much use moving forward, and we've got plenty of safe performance
improvements from the last 30 years of hardware advances.

src/xc.c

@@ -109,9 +109,6 @@ extern MouseInterface currentmouse;
 
 #ifdef SUN3_OS3_OR_OS4_IL
 #include "inln68k.h"
-#ifdef UNSAFE
-#include "fastinln68k.h"
-#endif
 #endif
 
 typedef struct conspage ConsPage;
@@ -230,10 +227,6 @@ void dispatch(void) {
 #endif
 #endif
 
-#ifdef UNSAFE
-  register int Save_D5_shift_amount;
-#endif
-
   /* OP_FN_COMMON arguments */
 
   DefCell *fn_defcell;
@@ -258,10 +251,6 @@ void dispatch(void) {
   table = (InstPtr *)compute_dispatch_table();
 #endif
 
-#ifdef UNSAFE
-  Save_D5_shift_amount = 15;
-#endif
-
 #ifdef I386
   goto setup_table;
 #else
@@ -1481,10 +1470,6 @@ setup_table:
 #ifndef ISC
   SaveD6 = 0;
 
-#ifdef UNSAFE
-  Save_D5_shift_amount = 15;
-#endif
-
   {
     int i;
     for (i = 0; i < 256; i++) { table[i] = (InstPtr)op_ufn; };