Remove ENABLE_AERIAL switch in aerial bindings

As is visible at the top of the patch, for compiling aerial_lib (the
binding FAPI-Aerial), we always add ENABLE_AERIAL. Thus, all the code
within ENABLE_AERIAL will be compiled; we can also simply take it out.

nfapi/oai_integration/aerial/fapi_nvIPC.h

@@ -29,7 +29,6 @@
 * \note
 * \warning
  */
-#ifdef ENABLE_AERIAL
 #ifndef OPENAIRINTERFACE_FAPI_NVIPC_H
 #define OPENAIRINTERFACE_FAPI_NVIPC_H
 
@@ -57,4 +56,3 @@ void set_config(nfapi_vnf_config_t *conf);
 int nvIPC_Init(nvipc_params_t);
 
 #endif // OPENAIRINTERFACE_FAPI_NVIPC_H
-#endif