Reasons for rename:
- Default value is
<datadir>/wallets
so calling it-walletsdir
instead of-walletdir
would be more internally consistent. - Directory can contain more than one wallet so plural makes sense
- This makes it harder to confuse
-walletdir
option with-wallet
option if we store wallets in their own directories as proposed in #11466 (comment) and implemented in https://github.com/bitcoin/bitcoin/pull/12216