Cleanup unused var warnings

Clean up compiling output so that actual issues can be spotted. Remove multiple
cases of unused parameter. Remove unused isActive at startup. (demod is started
regardless)

src/modules/modem/Modem.cpp

@@ -72,11 +72,11 @@ int Modem::getDefaultSampleRate() {
     return 200000;
 }
 
-void Modem::writeSetting(std::string setting, std::string value) {
+void Modem::writeSetting(std::string /* setting */, std::string /* value */) {
     // ...
 }
 
-std::string Modem::readSetting(std::string setting) {
+std::string Modem::readSetting(std::string /* setting */) {
     return "";
 }