Removed redundant ref from 1st Orekit day.

publications.html

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       Journot M., Frouvelle N., Udroiu C. I., Barbulescu L. F., Hogoiu O. M., Teodorescu M., Janer A., Sola Romeu P.<br/>
       May 2018 – 15th International Conference on Space Operations (SpaceOps), AIAA, Marseille, 2018</p>
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-    <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://orekit.org/doc/orekit-day/2017/6-orekit-at-the-us-naval-research-laboratory.pdf">Orekit at the U.S. Naval Research Lab</a><br/>
-      Ward E. M.<br/>
-      November 2017 – Orekit Day, Toulouse, France, November 2017</p>
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     <p><span class="fa-li fa-lg fa fa-gears"></span><a href="https://apps.dtic.mil/sti/pdfs/AD1016476.pdf">On directional measurement representation in orbit determination</a><br/>
       Ward E. M., Carbott G.<br/>