Port to libhandy 1

This ports Calls to libhandy 1 and drops the embedded HdyAvatar in favor
of the libhandy one.

Fixes https://source.puri.sm/Librem5/calls/-/issues/172

src/calls-call-display.c

@@ -31,9 +31,6 @@
 #include <glib-object.h>
 #include <glib.h>
 
-#define HANDY_USE_UNSTABLE_API
-#include <handy.h>
-
 struct _CallsCallDisplay
 {
   GtkOverlay parent_instance;