Remove --emulate-rf option and corresponding code

With the RFemulator, there is no need for a dedicated --emulate-rf
option anymore. For all uses of --emulate-rf, RFemulator should be used
instead.

executables/lte-softmodem.h

@@ -127,7 +127,6 @@ extern int sync_var;
 extern int transmission_mode;
 extern double cpuf;
 
-extern int emulate_rf;
 extern int numerology;
 extern int usrp_tx_thread;