fix: remove deprecated cutouts directory

[daniel-rdt]

Changes proposed in this Pull Request

This PR proposes to remove the deprecated cutouts directory from PyPSA-Eur. The cutouts directory is deprecated since 151f603 and cutouts are saved under the data directory instead.

All stale references are removed in this PR. Input cutouts for the build path of country_hdd and country_runoff are additionally updated to the new cutout location in which cutouts need to either be placed or should be build by the workflow with cutout data source build for europe-1940-2024-era5.nc.

Checklist

Required:

• Changes are tested locally and behave as expected.
• Code and workflow changes are documented.
• A release note entry is added to doc/release_notes.md.
• The description is human-written and any AI-generated content is marked.

If applicable:

• Changes in configuration options are reflected in scripts/lib/validation.
• For new data sources or versions, these instructions have been followed.
• New rules are documented in the appropriate doc/*.md files.