twMDelSpot( nHndl, nSpotNo )
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     Delete a hot spot structure from the TSDWIN internal array. The
     handle and spot number are values returned from twMOpen() or
     twMSetRegions(). The programmer is responsible for determining the
     structure of any spot definitions in the calling function.
     twMAddSpot() can hold either an array of spots or a single spot in
     each handle location.

       Arguments:

     nHndl   - 'N' The handle in the internal array where the regions
                   are stored.

     nSpotNo - 'N' The element in the region array for the handle you
                   wish to delete.

       Return:

     The length of the internal TSDWIN region array.

       Example:

     twMDelSpot( aRegions[ 1 ], nSpotNo )