sethdseed and importmulti are not available for descriptor wallets, so when doing descriptor wallet tests, use importdescriptors instead
The keypool size when using descriptor wallets is unaffected for Bitcoin ABC, because our descriptors wallets have only the p2pkh keys.
This is a backport of core#18788 [7/15]
https://github.com/bitcoin/bitcoin/pull/18788/commits/25bc5dccbfd52691adca6edd418dd54290300c28