Spec.dependencies: allow to filter on virtuals (#47284)

Signed-off-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

lib/spack/llnl/util/lang.py

@@ -871,15 +871,6 @@ class UnhashableArguments(TypeError):
     """Raise when an @memoized function receives unhashable arg or kwarg values."""
 
 
-def enum(**kwargs):
-    """Return an enum-like class.
-
-    Args:
-        **kwargs: explicit dictionary of enums
-    """
-    return type("Enum", (object,), kwargs)
-
-
 T = TypeVar("T")