Clarify the relationship between a Window object and its associated Expr.

FossilOrigin-Name: 0cd55e98a478740032f5569ddc00fa5b0e063e90db6e00ac7598c9b7c2fffeee
diff --git a/src/sqliteInt.h b/src/sqliteInt.h
index 7d4c3ea..cd702ce 100644
--- a/src/sqliteInt.h
+++ b/src/sqliteInt.h
@@ -3488,7 +3488,6 @@
 
   Expr *pFilter;
   FuncDef *pFunc;
-  int nArg;
 
   int iEphCsr;            /* Temp table used by this window */
   int regAccum;
@@ -3513,7 +3512,7 @@
 int sqlite3WindowRewrite(Parse*, Select*);
 int sqlite3ExpandSubquery(Parse*, struct SrcList_item*);
 void sqlite3WindowUpdate(Parse*, Window*, Window*, FuncDef*);
-Window *sqlite3WindowDup(sqlite3 *db, Window *p);
+Window *sqlite3WindowDup(sqlite3 *db, Expr *pOwner, Window *p);
 
 /*
 ** Assuming zIn points to the first byte of a UTF-8 character,