Remove --mmu-dirty command line flag

With the addition of Svadu support, the --mmu-dirty flag
no longer controls behavior of A/D updates to PTEs. Remove
the flag.

spike_main/spike.cc

@@ -70,7 +70,6 @@ static void help(int exit_code = 1)
   fprintf(stderr, "  --initrd=<path>       Load kernel initrd into memory\n");
   fprintf(stderr, "  --bootargs=<args>     Provide custom bootargs for kernel [default: console=hvc0 earlycon=sbi]\n");
   fprintf(stderr, "  --real-time-clint     Increment clint time at real-time rate\n");
-  fprintf(stderr, "  --mmu-dirty           Enable hardware management of PTE accessed and dirty bits\n");
   fprintf(stderr, "  --triggers=<n>        Number of supported triggers [default 4]\n");
   fprintf(stderr, "  --dm-progsize=<words> Progsize for the debug module [default 2]\n");
   fprintf(stderr, "  --dm-sba=<bits>       Debug system bus access supports up to "
@@ -440,7 +439,6 @@ int main(int argc, char** argv)
   parser.option(0, "initrd", 1, [&](const char* s){initrd = s;});
   parser.option(0, "bootargs", 1, [&](const char* s){cfg.bootargs = s;});
   parser.option(0, "real-time-clint", 0, [&](const char UNUSED *s){cfg.real_time_clint = true;});
-  parser.option(0, "mmu-dirty", 0, [&](const char UNUSED *s){cfg.dirty_enabled = true;});
   parser.option(0, "triggers", 1, [&](const char *s){cfg.trigger_count = atoul_safe(s);});
   parser.option(0, "extlib", 1, [&](const char *s){
     void *lib = dlopen(s, RTLD_NOW | RTLD_GLOBAL);