descriptors: addr() and raw() should return false for ToPrivateString

They don't have any private data and they can't be nested so they
should return false for ToPrivateString.

src/script/descriptor.cpp

@@ -612,7 +612,7 @@ public:
         return AddChecksum(ret);
     }
 
-    bool ToPrivateString(const SigningProvider& arg, std::string& out) const final
+    bool ToPrivateString(const SigningProvider& arg, std::string& out) const override
     {
         bool ret = ToStringHelper(&arg, out, StringType::PRIVATE);
         out = AddChecksum(out);
@@ -698,6 +698,7 @@ public:
         return OutputTypeFromDestination(m_destination);
     }
     bool IsSingleType() const final { return true; }
+    bool ToPrivateString(const SigningProvider& arg, std::string& out) const final { return false; }
 };
 
 /** A parsed raw(H) descriptor. */
@@ -718,6 +719,7 @@ public:
         return OutputTypeFromDestination(dest);
     }
     bool IsSingleType() const final { return true; }
+    bool ToPrivateString(const SigningProvider& arg, std::string& out) const final { return false; }
 };
 
 /** A parsed pk(P) descriptor. */