remove grid variable and attrs in dfmt.open_dataset_delft3d4()

[MPWeeber]

When opening a delft3d4 netcdf with dfmt.open_dataset_delft3d4(), the grid variable is not removed. When writing this uds to a netcdf file with uds.ugrid.to_netcdf() the resulting file cannot be opened by quickplot. When removing the variable, quickplot still warns about grid attrs being present in data variables. These should also be removed:

file_nc = "trim-Model-k01-with topography-eco.nc"
uds = dfmt.open_dataset_delft3d4(file_nc)

uds = uds.drop_vars(["MFTAVG","MORAVG","grid"])

#write
uds.ugrid.to_netcdf("test2.nc")
# results in QP conflicting file

#workaround (do for all variables)
ds = uds.ugrid.to_dataset()
del ds["RSEDEQ"].attrs["grid"]
print(ds["RSEDEQ"])
ds.to_netcdf("netcdf/file/nc")

QP warnings:

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Cannot find mesh "grid"; ignoring mesh/location attributes on "RHO".
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Cannot find mesh "grid"; ignoring mesh/location attributes on "VICUV".
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Cannot find mesh "grid"; ignoring mesh/location attributes on "WS".