/usr/lib/x86_64-linux-gnu/vala-panel/applets/xembed.plugin is in vala-panel-plugins-wnck 0.3.65-0ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Module=xembed
Name[ru]=Трей XEmbed
Name=XEmbed Tray
Description[ru]=Устаревший трей XEmbed
Description=Old XEmbed-based tray
X-ValaPanel-OnePerSystem=true;
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