Get rid of class GprsCodingScheme

We have same kind of object splitted into two layers, in coding_scheme
and gprs_coding_scheme. Let's merge them together and get rid of the
class, which is not really useful because it's only a set of functions
operating on one enum value.

This change also fixes gcc 10.1.0 error about memseting a complex type
in rlc.h init().

Change-Id: Ie9ce2144ba9e8dbba9704d4e0000a2929e3e41df
diff --git a/src/pcu_main.cpp b/src/pcu_main.cpp
index a33b655..3912204 100644
--- a/src/pcu_main.cpp
+++ b/src/pcu_main.cpp
@@ -31,12 +31,12 @@
 #include <signal.h>
 #include <sched.h>
 #include <bts.h>
-#include <gprs_coding_scheme.h>
 #include <osmocom/pcu/pcuif_proto.h>
 #include "gprs_bssgp_pcu.h"
 
 extern "C" {
 #include "pcu_vty.h"
+#include "coding_scheme.h"
 #include <osmocom/gprs/gprs_bssgp.h>
 #include <osmocom/gprs/gprs_ns.h>
 #include <osmocom/vty/telnet_interface.h>