cpp-netlib: unpin boost169

pkgs/development/libraries/cpp-netlib/default.nix

···
 
   cmakeFlags = [
     "-DCPP-NETLIB_BUILD_SHARED_LIBS=ON"
+    # fatal error: 'boost/asio/stream_socket_service.hpp' file not found
+    "-DCPP-NETLIB_BUILD_EXAMPLES=OFF"
+    "-DCPP-NETLIB_BUILD_TESTS=OFF"
   ];
 
   # Most tests make network GET requests to various websites

pkgs/top-level/all-packages.nix

···
 
   cpp-ipfs-http-client = callPackage ../development/libraries/cpp-ipfs-http-client { };
 
-  cpp-netlib = callPackage ../development/libraries/cpp-netlib {
-    boost = boost169; # fatal error: 'boost/asio/stream_socket_service.hpp' file not found
-  };
+  cpp-netlib = callPackage ../development/libraries/cpp-netlib { };
 
   cpp-jwt = callPackage ../development/libraries/cpp-jwt { };