mgmt: hawkbit: remove hb_context.status_buffer_size

remove hb_context.status_buffer_size and replace it with
sizeof(hb_context.status_buffer), because hb_context.status_buffer_size
is never set.

Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>
(cherry picked from commit 1bea938c9f8c02190daa582144a3cff65e1a12f4)
diff --git a/subsys/mgmt/hawkbit/hawkbit.c b/subsys/mgmt/hawkbit/hawkbit.c
index a4b1a8d..c2bc169 100644
--- a/subsys/mgmt/hawkbit/hawkbit.c
+++ b/subsys/mgmt/hawkbit/hawkbit.c
@@ -81,7 +81,6 @@
 	uint8_t *response_data;
 	int32_t json_action_id;
 	size_t url_buffer_size;
-	size_t status_buffer_size;
 	struct hawkbit_download dl;
 	struct http_request http_req;
 	struct flash_img_context flash_ctx;
@@ -845,7 +844,7 @@
 
 		ret = json_obj_encode_buf(json_cfg_descr, ARRAY_SIZE(json_cfg_descr), &cfg,
 					  hb_context.status_buffer,
-					  hb_context.status_buffer_size - 1);
+					  sizeof(hb_context.status_buffer));
 		if (ret) {
 			LOG_ERR("Can't encode the JSON script (HAWKBIT_CONFIG_DEVICE): %d", ret);
 			return false;
@@ -875,7 +874,7 @@
 
 		ret = json_obj_encode_buf(json_close_descr, ARRAY_SIZE(json_close_descr), &close,
 					  hb_context.status_buffer,
-					  hb_context.status_buffer_size - 1);
+					  sizeof(hb_context.status_buffer));
 		if (ret) {
 			LOG_ERR("Can't encode the JSON script (HAWKBIT_CLOSE): %d", ret);
 			return false;
@@ -922,7 +921,7 @@
 
 		ret = json_obj_encode_buf(json_dep_fbk_descr, ARRAY_SIZE(json_dep_fbk_descr),
 					  &feedback, hb_context.status_buffer,
-					  hb_context.status_buffer_size - 1);
+					  sizeof(hb_context.status_buffer));
 		if (ret) {
 			LOG_ERR("Can't encode the JSON script (HAWKBIT_REPORT): %d", ret);
 			return ret;