Fix a bug in the threadtest4.c program. Remove the keyinfo cache as it provides

minimal performance improvements, and then only at SQL preparation time, not
at runtime, and it has problems with data races in shared-cache mode.  We might
later add the keyinfo cache back but only enable it when shared-cache mode
is off.

FossilOrigin-Name: b7489f9451628c68f1dfc1d457fc161a0921c631

src/sqliteInt.h

@@ -1784,7 +1784,6 @@ struct Index {
   u8 *aSortOrder;          /* for each column: True==DESC, False==ASC */
   char **azColl;           /* Array of collation sequence names for index */
   Expr *pPartIdxWhere;     /* WHERE clause for partial indices */
-  KeyInfo *pKeyInfo;       /* A KeyInfo object suitable for this index */
   int tnum;                /* DB Page containing root of this index */
   LogEst szIdxRow;         /* Estimated average row size in bytes */
   u16 nKeyCol;             /* Number of columns forming the key */