Say your chart is included in the div with "chart1" as id, you can hide the first label of the label using:
$("div#chart1 div.jqplot-yaxis div.jqplot-yaxis-tick:nth-child(1)").css('display','none');
Where div#chart1 represents your chart, div.jqplot-yaxis your container with yaxis and jqplot-yaxis-tick:nth-child(x) gadgets jqplot-yaxis-tick:nth-child(x) x-th ticks in this container (it goes from 1 to the number of ticks - where 1 represents ticks at the bottom of your chart)
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