The inclusion of the _raw field is down to the search itself, so you can have it excluded by using the fields command, i.e.
sourcetype=blah | fields - _raw
or to exclude all hidden fields
sourcetype=blah | fields - _*
If you really only need specific fields, then use the table command to specify which fields you want displayed,
i.e.
sourcetype=blah | table source, sourcetype, host, index
The dashes at the top underline the header row, do you not want any column headings? Without the _raw field you will only have a table of fields and the header row is surely useful?
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