Clear the history information recorded with the observation.
EXAMLE
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0> clrhist

CONTEXT
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It is normal for UV FITS files to contain an extensive processing
history, such as that recorded by AIPS. While Difmap adds very little
to this Difmap does preserve it and passes it on to output UV FITS
and map image FITS files, and while in some cases it might be useful,
in others it may significantly enlarge data files for no good reason.

The 'clrhist' command clears the currently recorded history.

RELATED COMMANDS
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addhist  - Add a new line of history.
showhist - Display the currently recorded history.