Remove sign change on vertical velocity

Author: fluidnumerics-joe

src/parcels/_core/fieldset.py

@@ -284,9 +284,6 @@ def from_fesom2(ds: ux.UxDataset):
             fields["V"].units = Geographic()
 
             if "W" in ds.data_vars:
-                ds["W"] -= ds[
-                    "W"
-                ]  # Negate W to convert from up positive to down positive (as that's the direction of positive z)
                 fields["W"] = Field("W", ds["W"], grid)
                 fields["UVW"] = VectorField("UVW", fields["U"], fields["V"], fields["W"])
             else: