_load should remove type_field from data before shema load

Leaving the type field in the data dictionary generates errors when calling shema.load.

errors={'_schema': ['Unknown field name type.']})

It could be pop instead of get, but this would modify the data, so we have to copy the dict before.

Possible implementation:

    def _load(self, data, partial=None):
        data_copy = dict(data)
        data_type = data_copy.pop(self.type_field)
        [...]
        return schema.load(data_copy, many=False, partial=partial)

What do you think?

[maximkulkin]

@lafrech Ok, I got this. Thanks for reporting and helping with repro!

[maximkulkin]

Although I prefer forgiving schemas (ones that ignore extra fields) I agree that it makes sense to remove added type attribute. I will look into this.