Enforce sapling activation at height=1

We used to have the -ac_sapling option which defaulted to one, now we
enforce that it must always be one, it cannot be changed and is no
longer a CLI option.

src/hush_utils.h

@@ -2092,7 +2092,7 @@ void hush_args(char *argv0)
         }
         
         // HUSH will always be The First Pure Sapling Coin, no Sprout JoinSplits in our history! ;)
-        ASSETCHAINS_SAPLING = GetArg("-ac_sapling", 1);
+        ASSETCHAINS_SAPLING = 1; // GetArg("-ac_sapling", 1);
         if (ASSETCHAINS_SAPLING == -1)
         {
             ASSETCHAINS_OVERWINTER = GetArg("-ac_overwinter", -1);