copernicusmarine remove hardcoded offset for "rean-d" datasets

[veenstrajelmer]

A 12 hour offset was implemented for copernicusmarine "P1D-m" (daily means) datasets in #878. However, not all datasets are named according to the conventions, for instance "med-cmcc-*-rean-d" datasets in https://data.marine.copernicus.eu/product/MEDSEA_MULTIYEAR_PHY_006_004/services. For these specific datasets, an additional hard-coded filter for "rean-d" was also implemented. Remove this once the datasets are renamed to keep the code clean.

Track these pages to know when the datasets have been renamed to the conventions:

• https://data.marine.copernicus.eu/product/MEDSEA_MULTIYEAR_PHY_006_004/notifications
• https://marine.copernicus.eu/user-corner/product-roadmap/transition-information?roadmap_category=All&field_date=&field_ocean=All&field_omi_family=All&field_roadmap_item_status=All&field_product_kind=All&product=&text=006_004&id