Remove preview picture from share view page for wallabag#1875

Essentially, same as commit 038fccd for single entry views. From that commit:
> Showing the preview picture usually leads to showing a duplicate
> image, and frequently leads to showing duplicate images directly
> adjacent to each other.

src/Wallabag/CoreBundle/Resources/views/themes/common/Entry/share.html.twig

@@ -29,9 +29,6 @@
             <h1>{{ entry.title|e|raw }}</h1>
             <a href="{{ entry.url|e }}" target="_blank" rel="noopener" title="{{ 'entry.view.original_article'|trans }} : {{ entry.title|e|raw }}" class="tool">{{ entry.domainName|removeWww }}</a>
             <p class="shared-by">{{ "entry.public.shared_by_wallabag"|trans({'%wallabag_instance%': url('homepage'), '%username%': entry.user.username})|raw }}.</p>
-            {% if entry.previewPicture is not null %}
-                <img class="preview" src="{{ entry.previewPicture }}" alt="{{ entry.title|striptags|e('html_attr') }}" />
-            {% endif %}
         </header>
         <article class="block">
             {{ entry.content | raw }}