stone/unexplored glyph follow-up

typo

include/decl.h

@@ -1199,7 +1199,6 @@ struct const_globals {
     const struct obj zeroobj;      /* used to zero out a struct obj */
     const struct monst zeromonst;  /* used to zero out a struct monst */
     const anything zeroany;        /* used to zero out union any */
-    const struct rm zerorm;        /* used to zero out struct rm */
 };
 
 E const struct const_globals cg;