Remove ability to specify some settings on the survey sheet

[lindsay-stevens]

In workbook_to_json there's a code block that allows specifying some settings on the survey sheet. There does not seem to be any tests or docs for that behaviour. It was added in this commit (2012-01-09). So the proposal is to delete the code block, because it seems unlikely that anyone would use that functionality, and it is not consistent with long standing documentation about using the survey and settings sheets.

https://github.com/XLSForm/pyxform/blob/v4.2.0/pyxform/xls2json.py#L745-L750

# Check if the question is actually a setting specified
# on the survey sheet
settings_type = aliases.settings_header.get(question_type)
if settings_type:
    json_dict[settings_type] = str(row.get(constants.NAME))
    continue

The aliases.settings_header dict is currently:

settings_header = {
    "form_title": constants.TITLE,
    "set_form_title": constants.TITLE,
    "form_id": constants.ID_STRING,
    "set_form_id": constants.ID_STRING,
    "prefix": constants.COMPACT_PREFIX,
}

So users could write a form like the following, but would only work for the settings keys in the above dict:

| survey |
| | type       | name    | label |
| | form_title | my_form |       |
| | text       | q1      | Q1    |