Omit all use of Expr nodes for TK_AS, as those nodes no longer served a useful

purpose and in fact interferred with the query planner.

FossilOrigin-Name: 7ab0b258eabfcfb7f1b0bd1b12e166d2f267823d

src/sqliteInt.h

@@ -2135,6 +2135,7 @@ struct Expr {
 #define EP_ConstFunc 0x080000 /* A SQLITE_FUNC_CONSTANT or _SLOCHNG function */
 #define EP_CanBeNull 0x100000 /* Can be null despite NOT NULL constraint */
 #define EP_Subquery  0x200000 /* Tree contains a TK_SELECT operator */
+#define EP_Alias     0x400000 /* Is an alias for a result set column */
 
 /*
 ** Combinations of two or more EP_* flags