Refactor: Remove support for multiple protocols

This removes the boilerplate code supporting more than one RPC protocol as it
was becoming hard to maintain and we probably won't ever need it.

src/nvim/os/server.c

@@ -5,7 +5,6 @@
 
 #include <uv.h>
 
-#include "nvim/os/channel_defs.h"
 #include "nvim/os/channel.h"
 #include "nvim/os/server.h"
 #include "nvim/os/os.h"
@@ -25,8 +24,6 @@ typedef enum {
 } ServerType;
 
 typedef struct {
-  // Protocol for channels established through this server
-  ChannelProtocol protocol;
   // Type of the union below
   ServerType type;
 
@@ -59,8 +56,7 @@ void server_init()
     free(listen_address);
   }
 
-  server_start((char *)os_getenv("NEOVIM_LISTEN_ADDRESS"),
-               kChannelProtocolMsgpack);
+  server_start((char *)os_getenv("NEOVIM_LISTEN_ADDRESS"));
 }
 
 void server_teardown()
@@ -80,7 +76,7 @@ void server_teardown()
   });
 }
 
-void server_start(char *endpoint, ChannelProtocol prot)
+void server_start(char *endpoint)
 {
   char addr[ADDRESS_MAX_SIZE];
 
@@ -101,8 +97,6 @@ void server_start(char *endpoint, ChannelProtocol prot)
   Server *server = xmalloc(sizeof(Server));
   char ip[16], *ip_end = strrchr(addr, ':');
 
-  server->protocol = prot;
-
   if (!ip_end) {
     ip_end = strchr(addr, NUL);
   }
@@ -229,7 +223,7 @@ static void connection_cb(uv_stream_t *server, int status)
     return;
   }
 
-  channel_from_stream(client, srv->protocol);
+  channel_from_stream(client);
 }
 
 static void free_client(uv_handle_t *handle)