ui: Remove/adapt some old code for a big UI refactor

- Remove abstract_ui global, now it is always active
- Remove some terminal handling code
- Remove unused functions
- Remove HAVE_TGETENT/TERMINFO/TERMIOS/IOCTL #ifdefs
- Remove tgetent/terminfo from version.c
- Remove curses/terminfo dependencies
- Only start/stop termcap when starting/exiting the program
- msg_use_printf will return true if there are no attached UIs(
  messages will be written to stdout)
- Remove `ex_winpos`(implement `:winpos` with `ex_ni`)

src/nvim/msgpack_rpc/channel.c

@@ -103,9 +103,7 @@ void channel_init(void)
     channel_from_stdio();
   }
 
-  if (abstract_ui) {
-    remote_ui_init();
-  }
+  remote_ui_init();
 }
 
 /// Teardown the module
@@ -176,13 +174,6 @@ void channel_from_stream(uv_stream_t *stream)
   channel->data.streams.uv = stream;
 }
 
-bool channel_exists(uint64_t id)
-{
-  Channel *channel;
-  return (channel = pmap_get(uint64_t)(channels, id)) != NULL
-    && !channel->closed;
-}
-
 /// Sends event/arguments to channel
 ///
 /// @param id The channel id. If 0, the event will be sent to all
@@ -665,10 +656,7 @@ static void on_stdio_close(Event e)
 
 static void free_channel(Channel *channel)
 {
-  if (abstract_ui) {
-    remote_ui_disconnect(channel->id);
-  }
-
+  remote_ui_disconnect(channel->id);
   pmap_del(uint64_t)(channels, channel->id);
   msgpack_unpacker_free(channel->unpacker);
 

src/nvim/msgpack_rpc/helpers.c

@@ -295,22 +295,6 @@ void msgpack_rpc_from_dictionary(Dictionary result, msgpack_packer *res)
   }
 }
 
-/// Finishes the msgpack-rpc call with an error message.
-///
-/// @param msg The error message
-/// @param res A packer that contains the response
-void msgpack_rpc_error(char *msg, msgpack_packer *res)
-  FUNC_ATTR_NONNULL_ALL
-{
-  size_t len = strlen(msg);
-
-  // error message
-  msgpack_pack_bin(res, len);
-  msgpack_pack_bin_body(res, msg, len);
-  // Nil result
-  msgpack_pack_nil(res);
-}
-
 /// Handler executed when an invalid method name is passed
 Object msgpack_rpc_handle_missing_method(uint64_t channel_id,
                                          uint64_t request_id,