Remove `components` and `ancestry`, and make `prune_dirs` Path-only

[snejus]

Part of: #1409

Depends on: #6809.

Problem

beets.util.components, beets.util.ancestry, and the byte-compatible prune_dirs implementation duplicate behavior that Path already provides. Keeping these helpers after runtime paths are Path-native makes utility code harder to reason about and leaves another place where bytes can enter filesystem logic.

Expected behavior

• Replace components callers with Path.parts or equivalent local Path operations.
• Replace ancestry callers with Path.parents or equivalent local Path operations.
• Make prune_dirs accept Path for both the target directory and optional root.
• Keep clutter matching behavior unchanged.
• Remove tests that only validate the deleted compatibility helpers, while preserving coverage for the behavior that still exists.

Suggested fix

Remove the obsolete decomposition helpers first, then simplify prune_dirs around Path.exists, Path.iterdir, Path.parents, and shutil.rmtree.

Acceptance criteria

• No production or test code imports components or ancestry.
• prune_dirs callers pass Path.
• Directory pruning behavior remains covered by tests.
• poe test and poe lint pass with coverage at or above 80%.