Remove uses of fPruneMode in wallet code

This commit does not change behavior.

src/interfaces/chain.h

@@ -155,6 +155,9 @@ public:
 
     //! Pool min fee.
     virtual CFeeRate mempoolMinFee() = 0;
+
+    //! Check if pruning is enabled.
+    virtual bool getPruneMode() = 0;
 };
 
 //! Interface to let node manage chain clients (wallets, or maybe tools for