rm 'Edit structure' button (#758)

This resolves #758 (closed).

GUI/images/edit.svg

-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<svg
-   inkscape:version="1.1 (c68e22c387, 2021-05-23)"
-   sodipodi:docname="edit.svg"
-   id="svg4"
-   viewBox="0 0 24 24"
-   height="24"
-   width="24"
-   version="1.1"
-   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
-   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
-   xmlns="http://www.w3.org/2000/svg"
-   xmlns:svg="http://www.w3.org/2000/svg"
-   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
-   xmlns:cc="http://creativecommons.org/ns#"
-   xmlns:dc="http://purl.org/dc/elements/1.1/">
-  <metadata
-     id="metadata10">
-    <rdf:RDF>
-      <cc:Work
-         rdf:about="">
-        <dc:format>image/svg+xml</dc:format>
-        <dc:type
-           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
-      </cc:Work>
-    </rdf:RDF>
-  </metadata>
-  <defs
-     id="defs8">
-    <inkscape:path-effect
-       effect="fill_between_many"
-       method="originald"
-       linkedpaths="#path47568,0,1"
-       id="path-effect47736" />
-    <inkscape:path-effect
-       effect="fill_between_many"
-       method="originald"
-       linkedpaths="#path47568,0,1"
-       id="path-effect47760" />
-  </defs>
-  <sodipodi:namedview
-     inkscape:current-layer="svg4"
-     inkscape:window-maximized="0"
-     inkscape:window-y="0"
-     inkscape:window-x="571"
-     inkscape:cy="10.859634"
-     inkscape:cx="9.3321706"
-     inkscape:zoom="47.791668"
-     showgrid="false"
-     id="namedview6"
-     inkscape:window-height="1561"
-     inkscape:window-width="2637"
-     inkscape:pageshadow="2"
-     inkscape:pageopacity="0"
-     guidetolerance="10"
-     gridtolerance="10"
-     objecttolerance="10"
-     borderopacity="1"
-     bordercolor="#666666"
-     pagecolor="#ffffff"
-     inkscape:pagecheckerboard="0" />
-  <path
-     style="fill:#838686;fill-opacity:1;stroke-width:1.50205"
-     id="path2"
-     d="m 22.456843,18.933379 -20.6625972,0.05866 v 2.68601 l 20.6625972,0.05866 z"
-     sodipodi:nodetypes="ccccc" />
-  <path
-     style="fill:#838686;fill-opacity:1;stroke-width:1.39642"
-     id="path2-5"
-     d="m 16.543648,3.053311 -8.6331942,9.417549 2.7513672,2.554907 8.75337,-9.3059537 z"
-     sodipodi:nodetypes="ccccc" />
-  <path
-     style="fill:#838686;fill-opacity:1;stroke-width:0.0983853"
-     d="m 6.0877442,16.391465 c 0.040174,-0.350234 1.5540236,-3.567398 1.6456489,-3.553913 0.06025,0.0089 0.4396847,0.453438 1.1245006,1.064663 l 1.5171343,1.4461 -3.7707868,2.113231 C 4.9089687,18.411614 6.0768418,16.486521 6.0877442,16.391465 Z"
-     id="path6974"
-     sodipodi:nodetypes="ccccsc" />
-  <path
-     inkscape:original-d="M 0,0"
-     inkscape:path-effect="#path-effect47760"
-     d="M 0,0"
-     id="path47762" />
-</svg>