feat: remove redundant bool mpp flag

crates/cdk/src/mint/builder.rs

@@ -124,8 +124,8 @@ impl MintBuilder {
             let mpp_settings = MppMethodSettings {
                 method,
                 unit: unit.clone(),
-                mpp: true,
             };
+
             let mut mpp = self.mint_info.nuts.nut15.clone();
 
             mpp.methods.push(mpp_settings);

crates/cdk/src/nuts/nut15.rs

@@ -24,8 +24,6 @@ pub struct MppMethodSettings {
     pub method: PaymentMethod,
     /// Currency Unit e.g. sat
     pub unit: CurrencyUnit,
-    /// Multi part payment support
-    pub mpp: bool,
 }
 
 /// Mpp Settings