Remove unused MaybeSetAddrName

This logic is a no-op since it was introduced in commit
f9f5cfc506.

m_addr_name is never initialized to the empty string, because
ToStringIPPort never returns an empty string.

src/net.h

@@ -659,8 +659,6 @@ public:
     }
 
     std::string GetAddrName() const;
-    //! Sets the addrName only if it was not previously set
-    void MaybeSetAddrName(const std::string& addrNameIn);
 
     std::string ConnectionTypeAsString() const { return ::ConnectionTypeAsString(m_conn_type); }