Externify trycall() and replace many docall() calls with it

trycall() is a short docall() wrapper that is a no-op if the item is
already identified or the player has called the object type already. For
some reason, many calls to docall() did those same exact checks
beforehand.

This commit eliminates that redundancy by converting those calls into
trycall(), which is now made extern rather than local to do.c. No
behavior should be changed by this commit; I've checked that none of the
affected places could take a different code path now that the
oc_name_known and oc_uname checks are removed.

src/read.c

@@ -440,8 +440,7 @@ doread(void)
 
         /* yet another note: despite the fact that player will recognize
            the object type, don't make it become a discovery for hero */
-        if (!objects[otyp].oc_name_known && !objects[otyp].oc_uname)
-            docall(scroll);
+        trycall(scroll);
         return ECMD_TIME;
     } else if (otyp == CREDIT_CARD) {
         static const char *const card_msgs[] = {
@@ -631,8 +630,8 @@ doread(void)
         if (!objects[otyp].oc_name_known) {
             if (g.known)
                 learnscroll(scroll);
-            else if (!objects[otyp].oc_uname)
-                docall(scroll);
+            else
+                trycall(scroll);
         }
         scroll->in_use = FALSE;
         if (otyp != SCR_BLANK_PAPER)