wallet, rpc: Remove watchonly from RPCs

Descriptor wallets don't have a conception of watchonly within a wallet,
so remove all of these options and results from the RPCs

test/functional/wallet_basic.py

@@ -532,7 +532,6 @@ class WalletTest(BitcoinTestFramework):
         assert_equal(address_info['address'], "mneYUmWYsuk7kySiURxCi3AGxrAqZxLgPZ")
         assert_equal(address_info["scriptPubKey"], "76a9144e3854046c7bd1594ac904e4793b6a45b36dea0988ac")
         assert not address_info["ismine"]
-        assert not address_info["iswatchonly"]
         assert not address_info["isscript"]
         assert not address_info["ischange"]