Revert "fix crash on NULL gi.invent"

This reverts commit 378648bd9c.

The problem was triggered by marking the 'objlist' argument in
merge_choice() prototype with __attribute__((nonnull)) when it
shouldn't have been, then a followup which relied on that.  The
'objlist' argument might be Null.  Instead of passing its address to
force it to be non-Null, remove the attribute.

src/shk.c

@@ -152,7 +152,7 @@ money2u(struct monst* mon, long amount)
         mongold = splitobj(mongold, amount);
     obj_extract_self(mongold);
 
-    if (!merge_choice(&gi.invent, mongold)
+    if (!merge_choice(gi.invent, mongold)
             && inv_cnt(FALSE) >= invlet_basic) {
         You("have no room for the gold!");
         dropy(mongold);