Drop no longer used tmt.utils.listify()

I suppose it was replaced by other "listify me this" functions, but it's
no longer used.

tests/unit/test_utils.py

@@ -33,7 +33,6 @@
     filter_paths,
     git_add,
     inject_auth_git_url,
-    listify,
     public_git_url,
     validate_git_status,
     wait,
@@ -195,16 +194,6 @@ def test_inject_auth_git_url(monkeypatch) -> None:
         inject_auth_git_url('https://example.com/broken/something')
 
 
-def test_listify():
-    """ Check listify functionality """
-    assert listify(['abc']) == ['abc']
-    assert listify('abc') == ['abc']
-    assert listify('a b c') == ['a b c']
-    assert listify('a b c', split=True) == ['a', 'b', 'c']
-    assert listify({'a': 1, 'b': 2}) == {'a': [1], 'b': [2]}
-    assert listify({'a': 1, 'b': 2}, keys=['a']) == {'a': [1], 'b': 2}
-
-
 def test_config():
     """ Config smoke test """
     run = Path('/var/tmp/tmt/test')

tmt/utils.py

@@ -1935,30 +1935,6 @@ def ascii(text: Any) -> bytes:
     return unicodedata.normalize('NFKD', text).encode('ascii', 'ignore')
 
 
-def listify(
-        data: Union[tuple[Any, ...], list[Any], str, dict[Any, Any]],
-        split: bool = False,
-        keys: Optional[list[str]] = None) -> Union[list[Any], dict[Any, Any]]:
-    """
-    Ensure that variable is a list, convert if necessary
-    For dictionaries check all items or only those with provided keys.
-    Also split strings on white-space/comma if split=True.
-    """
-    separator = re.compile(r'[\s,]+')
-    if isinstance(data, tuple):
-        data = list(data)
-    if isinstance(data, list):
-        return fmf.utils.split(data, separator) if split else data
-    if isinstance(data, str):
-        return fmf.utils.split(data, separator) if split else [data]
-    if isinstance(data, dict):
-        for key in keys or data:
-            if key in data:
-                data[key] = listify(data[key], split=split)
-        return data
-    return [data]
-
-
 def copytree(
         src: Path,
         dst: Path,