[export] remove pdf export

Remove pdf export with extreme prejudice due to issues with build process.

Fixes https://github.com/nasa/openmct/issues/1217

platform/features/plot/res/templates/plot.html

@@ -23,11 +23,6 @@
       class="abs holder holder-plot has-control-bar">
     <div class="l-control-bar" ng-show="!plot.hideExportButtons">
          <span class="l-btn-set">
-            <a class="s-button t-export icon-download labeled first"
-               ng-click="plot.exportPDF()"
-               title="Export This View's Data as PDF">
-                PDF
-            </a>
             <a class="s-button t-export labeled"
                ng-click="plot.exportPNG()"
                title="Export This View's Data as PNG">