remove unnecessary function declaration

has been introduced in commit 365ca71a

openair2/ENB_APP/CONTROL_MODULES/MAC/flexran_agent_mac.c

@@ -40,8 +40,6 @@
 
 #include "log.h"
 
-extern int flexran_get_harq_round(mid_t mod_id, uint8_t cc_id, mid_t ue_id);
-
 /*Flags showing if a mac agent has already been registered*/
 unsigned int mac_agent_registered[NUM_MAX_ENB];