No need to inherit from object

[DimitriPapadopoulos]

In Python 3, all classes implicitly inherit from object.

This fixes these DeepSource.io alerts:
https://deepsource.io/gh/DimitriPapadopoulos/zarr-python/issue/PYL-R0205/occurrences

TODO:

• Add unit tests and/or doctests in docstrings
• Add docstrings and API docs for any new/modified user-facing classes and functions
• New/modified features documented in docs/tutorial.rst
• Changes documented in docs/release.rst
• GitHub Actions have all passed
• Test coverage is 100% (Codecov passes)

[codecov]

Codecov Report

Merging #886 (c4c7524) into master (d9d460f) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #886   +/-   ##
=======================================
  Coverage   99.94%   99.94%           
=======================================
  Files          32       32           
  Lines       11214    11214           
=======================================
  Hits        11208    11208           
  Misses          6        6           

Impacted Files	Coverage Δ
zarr/convenience.py	100.00% <100.00%> (ø)
zarr/indexing.py	100.00% <100.00%> (ø)
zarr/sync.py	100.00% <100.00%> (ø)
zarr/tests/test_core.py	100.00% <100.00%> (ø)
zarr/tests/test_creation.py	100.00% <100.00%> (ø)
zarr/tests/test_hierarchy.py	100.00% <100.00%> (ø)
zarr/tests/test_storage.py	100.00% <100.00%> (ø)
zarr/tests/test_sync.py	100.00% <100.00%> (ø)
zarr/util.py	100.00% <100.00%> (ø)