Revert "sources(curl): disable curl --parallel by default"

This reverts commit 9bef57d.

sources/org.osbuild.curl

@@ -110,12 +110,6 @@ def curl_has_parallel_downloads():
     Return true if curl has all the support we needed for parallel downloading
     (this include --write-out "%{json}" too
     """
-    # Re-enable this once the failures in
-    # https://github.com/osbuild/osbuild-composer/pull/4247
-    # are understood
-    if os.getenv("OSBUILD_SOURCES_CURL_USE_PARALLEL") not in ["1", "yes", "true"]:
-        return False
-
     output = subprocess.check_output(["curl", "--version"], universal_newlines=True)
     first_line = output.split("\n", maxsplit=1)[0]
     m = re.match(r'^curl (\d+\.\d+\.\d+)', first_line)

sources/test/test_curl_source.py

@@ -170,9 +170,7 @@ def test_curl_download_many_chksum_validate(tmp_path, curl_parallel):
 
 
 @pytest.mark.parametrize("curl_parallel", [True, False], indirect=["curl_parallel"])
-def test_curl_download_many_retries(tmp_path, monkeypatch, curl_parallel):
-    monkeypatch.setenv("OSBUILD_SOURCES_CURL_USE_PARALLEL", "1")
-
+def test_curl_download_many_retries(tmp_path, curl_parallel):
     fake_httpd_root = tmp_path / "fake-httpd-root"
 
     with http_serve_directory(fake_httpd_root) as httpd:
@@ -352,14 +350,7 @@ def test_curl_gen_download_config_parallel(tmp_path, sources_module):
 
 
 @patch("subprocess.check_output")
-def test_curl_has_parallel_download(mocked_check_output, monkeypatch, sources_module):
-    # by default, --parallel is disabled
-    mocked_check_output.return_value = NEW_CURL_OUTPUT
-    assert not sources_module.curl_has_parallel_downloads()
-
-    # unless this environemnt is set
-    monkeypatch.setenv("OSBUILD_SOURCES_CURL_USE_PARALLEL", "1")
-
+def test_curl_has_parallel_download(mocked_check_output, sources_module):
     mocked_check_output.return_value = NEW_CURL_OUTPUT
     assert sources_module.curl_has_parallel_downloads()