[enhancement] --remove-metadata removes metadata independend of content (copyright violation)

[JoKalliauer]

I would like a option to only remove empty metadata.

It should delete RDF. RDF subtrees if empty, but it should keep

• <cc:license>
• <cc:attributionName>
• <cc:attributionURL>

Input 1

input1.svg.txt

<svg xmlns="http://www.w3.org/2000/svg" xmlns:cc="http://creativecommons.org/ns#" xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:xlink="http://www.w3.org/1999/xlink">
  <metadata id="metadata3879">
    <rdf:RDF>
      <cc:Work rdf:about="">
        <dc:format>image/svg+xml</dc:format>
        <dc:type rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
        <dc:title></dc:title>
      </cc:Work>
    </rdf:RDF>
  </metadata>
</svg>

source: https://de.wikipedia.org/wiki/Benutzer:Marsupilami/Inkscape-FAQ#Wie_erstelle_ich_eine_Datei_die_dem_Standard_SVG_1.1_entspricht? Author: Marsupilami Lizense: CC-BY-SA 3.0

Output1 as with --remove-metadata

Output1.svg.txt

<?xml version="1.0" encoding="UTF-8"?>
<svg xmlns="http://www.w3.org/2000/svg"/>

Input2

input2.svg.txt

<svg
  version="1.1"
  baseProfile="full"
  xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink">

<metadata>
  <rdf:RDF xmlns:cc="http://web.resource.org/cc/"
           xmlns:dc="http://purl.org/dc/elements/1.1/"
           xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <cc:Work rdf:about="">
        <dc:format>image/svg+xml</dc:format>
        <dc:type rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
        <cc:license rdf:resource="http://creativecommons.org/licenses/by-sa/3.0/" />
        <cc:attributionName rdf:resource="https://commons.wikimedia.org/wiki/User:Glrx"/>
        <cc:attributionURL rdf:resource="https://commons.wikimedia.org/w/index.php?title=File:SVG_Test_TextAlign.svg"/>
      </cc:Work>
    </rdf:RDF>
  </metadata>
</svg>

source: https://commons.wikimedia.org/w/index.php?title=File:SVG_Test_TextAlign.svg Author: Glrx Lizense: CC-BY-SA 3.0

Output2 should keep metadata since it would be a copyright violation

Output2.svg.txt

<?xml version="1.0" encoding="UTF-8"?>
<svg baseProfile="full" version="1.1" xmlns="http://www.w3.org/2000/svg">
 <metadata>
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
   <cc:Work xmlns:cc="http://web.resource.org/cc/" xmlns:dc="http://purl.org/dc/elements/1.1/">
    <dc:format>image/svg+xml</dc:format>
    <dc:type rdf:resource="http://purl.org/dc/dcmitype/StillImage"/>
    <cc:license rdf:resource="http://creativecommons.org/licenses/by-sa/3.0/"/>
    <cc:attributionName rdf:resource="https://commons.wikimedia.org/wiki/User:Glrx"/>
    <cc:attributionURL rdf:resource="https://commons.wikimedia.org/w/index.php?title=File:SVG_Test_TextAlign.svg"/>
   </cc:Work>
  </rdf:RDF>
 </metadata>
</svg>