context: delete unused label field

It's not necessary to store the label in the context type, instead use
the corresponding library function to get the current in-memory label
container.

The device label information is stored in-memory by libfdisk library
when creating a context or assigning a device.

Avoids possible incosistencies between libfdisk in-memory label and
python-libfdisk context type label information.

context.c

@@ -33,7 +33,6 @@ static PyObject *Context_new(PyTypeObject *type,
 
 	if (self) {
 		self->cxt = NULL;
-		self->lb = NULL;
 		self->tb = NULL;
 	}
 
@@ -96,7 +95,6 @@ static PyObject *Context_assign_device(ContextObject *self, PyObject *args, PyOb
 	/* XXX: readonly */
 	fdisk_assign_device(self->cxt, fname, 1);
 
-	self->lb = fdisk_get_label(self->cxt, NULL);
 	fdisk_get_partitions(self->cxt, &self->tb);
 
 	Py_INCREF(Py_None);

fdisk.h

@@ -25,7 +25,6 @@
 typedef struct {
 	PyObject_HEAD
 	struct fdisk_context		*cxt;
-	struct fdisk_label		*lb;
 	struct fdisk_table		*tb;
 } ContextObject;