wallet, refactor: Remove unused SetupGeneration

SetupGeneration was supposed to be the function that all SPKMs used
to setup automatic generation, but it didn't work out that way and
ended up being legacy only. It should be deleted at this point.

src/wallet/scriptpubkeyman.h

@@ -112,12 +112,6 @@ public:
      */
     virtual std::vector<WalletDestination> MarkUnusedAddresses(const CScript& script) { return {}; }
 
-    /** Sets up the key generation stuff, i.e. generates new HD seeds and sets them as active.
-      * Returns false if already setup or setup fails, true if setup is successful
-      * Set force=true to make it re-setup if already setup, used for upgrades
-      */
-    virtual bool SetupGeneration(bool force = false) { return false; }
-
     /* Returns true if HD is enabled */
     virtual bool IsHDEnabled() const { return false; }
 

src/wallet/wallet.cpp

@@ -2870,7 +2870,6 @@ std::shared_ptr<CWallet> CWallet::Create(WalletContext& context, const std::stri
 
         if ((wallet_creation_flags & WALLET_FLAG_EXTERNAL_SIGNER) || !(wallet_creation_flags & (WALLET_FLAG_DISABLE_PRIVATE_KEYS | WALLET_FLAG_BLANK_WALLET))) {
             walletInstance->SetupDescriptorScriptPubKeyMans();
-            // SetupDescriptorScriptPubKeyMans already calls SetupGeneration for us so we don't need to call SetupGeneration separately
         }
 
         if (chain) {