radioInterface: Remove unusued getRxGain()

Only the radioDevice->getRxGain() is called from inside
radioInterfaceMulti, so the API in radioInterface is not used at all.

Change-Id: Icc4e9a7ebfdafe7c72c535752a5e379d12592c9a

Transceiver52M/radioInterface.cpp

@@ -307,11 +307,6 @@ double RadioInterface::setRxGain(double dB, size_t chan)
   return mDevice->setRxGain(dB, chan);
 }
 
-double RadioInterface::getRxGain(size_t chan)
-{
-  return mDevice->getRxGain(chan);
-}
-
 /* Receive a timestamped chunk from the device */
 int RadioInterface::pullBuffer()
 {

Transceiver52M/radioInterface.h

@@ -109,9 +109,6 @@ public:
   /** set receive gain */
   double setRxGain(double dB, size_t chan = 0);
 
-  /** get receive gain */
-  double getRxGain(size_t chan = 0);
-
   /** drive transmission of GSM bursts */
   void driveTransmitRadio(std::vector<signalVector *> &bursts,
                           std::vector<bool> &zeros);