net: remove CService::ToString() use ToStringAddrPort() instead

Both methods do the same thing, so simplify to having just one.

`ToString()` is too generic in this case and it is unclear what it does,
given that there are similar methods:
`ToStringAddr()` (inherited from `CNetAddr`),
`ToStringPort()` and
`ToStringAddrPort()`.

src/netaddress.cpp

@@ -925,11 +925,6 @@ std::string CService::ToStringAddrPort() const
     }
 }
 
-std::string CService::ToString() const
-{
-    return ToStringAddrPort();
-}
-
 CSubNet::CSubNet():
     valid(false)
 {