Fix: Remove degree sign

It confuse ros diagnostics.

src/cpu_temperature_diagnostic.cc

@@ -32,7 +32,7 @@ void CpuTemperatureDiagnostic::diagnostics_callback(
         }
         std::string status_string = read.is_ok_ ? "OK" : "Error";
         stat.add(read.label_,
-                 std::to_string(int(read.temperature_)) + "°C " +
+                 std::to_string(int(read.temperature_)) + "C " +
                      status_string);
     }
     std::string summary =