Remove deprecated `datetime` functions

[kevinjqliu]

Feature Request / Improvement

To support python 3.12 in #1068, we had to ignore warnings for deprecated datetime functions.

Let's remove these deprecated functions from the codebase and also remove the warning filters.

https://github.com/apache/iceberg-python/blob/f2f428ec4d3c7d66b104ccaa235fc73fd0910bf3/pyproject.toml#L618-L619