Remove the unused xRename() method from the sqlite3_vfs object.

Add better documentation on the xCurrentTimeInt64() method.

FossilOrigin-Name: 51ec0e5432dd6849b83a3d969a018482eb3bb083

src/test6.c

@@ -813,7 +813,6 @@ static int crashEnableCmd(
     cfSleep,              /* xSleep */
     cfCurrentTime,        /* xCurrentTime */
     0,                    /* xGetlastError */
-    0,                    /* xRename */
     0,                    /* xCurrentTimeInt64 */
   };