Remove a dead (ownership-related) class (#3004)

## Changes

This PR trivially removes a dead class; this was detritus left over from
an intermediate version of the ownership mechanism that limited `Record`
to `dataclass` classes. However this limitation was removed prior to the
original code being merged (and the mechanism can be used with any
class).

src/databricks/labs/ucx/framework/owners.py

@@ -2,7 +2,7 @@
 from abc import ABC, abstractmethod
 from collections.abc import Callable, Iterable, Sequence
 from functools import cached_property
-from typing import ClassVar, Generic, Protocol, TypeVar, final
+from typing import Generic, TypeVar, final
 
 from databricks.sdk import WorkspaceClient
 from databricks.sdk.errors import NotFound
@@ -11,10 +11,6 @@
 logger = logging.getLogger(__name__)
 
 
-class DataclassInstance(Protocol):
-    __dataclass_fields__: ClassVar[dict]
-
-
 Record = TypeVar("Record")