tree-wide: get rid of strappend()

It's a special case of strjoin(), so no need to keep both. In particular
as typing strjoin() is even shoert than strappend().

src/machine/image-dbus.c

@@ -458,7 +458,7 @@ char *image_bus_path(const char *name) {
         if (!e)
                 return NULL;
 
-        return strappend("/org/freedesktop/machine1/image/", e);
+        return strjoin("/org/freedesktop/machine1/image/", e);
 }
 
 int image_node_enumerator(sd_bus *bus, const char *path, void *userdata, char ***nodes, sd_bus_error *error) {

src/machine/machine-dbus.c

@@ -1383,7 +1383,7 @@ char *machine_bus_path(Machine *m) {
         if (!e)
                 return NULL;
 
-        return strappend("/org/freedesktop/machine1/machine/", e);
+        return strjoin("/org/freedesktop/machine1/machine/", e);
 }
 
 int machine_node_enumerator(sd_bus *bus, const char *path, void *userdata, char ***nodes, sd_bus_error *error) {

src/machine/machine.c

@@ -22,6 +22,7 @@
 #include "machine.h"
 #include "mkdir.h"
 #include "parse-util.h"
+#include "path-util.h"
 #include "process-util.h"
 #include "serialize.h"
 #include "special.h"
@@ -53,7 +54,7 @@ Machine* machine_new(Manager *manager, MachineClass class, const char *name) {
                 goto fail;
 
         if (class != MACHINE_HOST) {
-                m->state_file = strappend("/run/systemd/machines/", m->name);
+                m->state_file = path_join("/run/systemd/machines", m->name);
                 if (!m->state_file)
                         goto fail;
         }