deposit.loader: Avoid unnecessary metadata json transformation

This reverts a small part of 777ea446 which introduced by mistake that
conversion into json.

swh/loader/package/deposit/loader.py

@@ -71,7 +71,7 @@ class DepositPackageInfo(BasePackageInfo):
         raw_info = {
             "origin": metadata["origin"],
             "origin_metadata": {
-                "metadata": json.dumps(metadata["metadata_dict"]),
+                "metadata": metadata["metadata_dict"],
                 "provider": metadata["provider"],
                 "tool": metadata["tool"],
             },

swh/loader/package/deposit/tests/test_deposit.py

@@ -301,7 +301,7 @@ def test_deposit_loading_ok_2(swh_config, requests_mock_datadir):
             "raw": {
                 "origin": {"type": "deposit", "url": url,},
                 "origin_metadata": {
-                    "metadata": json.dumps(raw_meta["metadata_dict"]),
+                    "metadata": raw_meta["metadata_dict"],
                     "provider": provider,
                     "tool": tool,
                 },