Remove try/except logic for importing Empty from queue library

Following [PEP8](https://peps.python.org/pep-0008/#package-and-module-names)
the Python 2 library `Queue` was renamed to `queue` in [Python 3](https://peps.python.org/pep-3108/#pep-8-violations-done).
Our try/except logic was to ensure the `Empty` class was imported without
error when running Python 2. Python 2 went EOL January 1st, 2020 and we
haven't supported Python 2 in a very long time. As such, it seems past time
to remove this relic.

tests/unit/test_graph.py

@@ -20,12 +20,7 @@
 from dbt.graph import NodeSelector, parse_difference
 from dbt.events.logging import setup_event_logger
 from dbt.mp_context import get_mp_context
-
-try:
-    from queue import Empty
-except ImportError:
-    from Queue import Empty
-
+from queue import Empty
 from .utils import config_from_parts_or_dicts, generate_name_macros, inject_plugin
 
 

tests/unit/test_linker.py

@@ -4,14 +4,9 @@
 from unittest import mock
 
 from dbt import compilation
-
-try:
-    from queue import Empty
-except ImportError:
-    from Queue import Empty
-
 from dbt.graph.selector import NodeSelector
 from dbt.graph.cli import parse_difference
+from queue import Empty
 
 
 def _mock_manifest(nodes):