Clean old code for multiselect (replaced with select2 plugin).

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htdocs/core/class/html.form.class.php

htdocs/includes/jquery/plugins/multiple-select/LICENSE

htdocs/includes/jquery/plugins/multiple-select/README.md

.../jquery/plugins/multiple-select/jquery.multiple.select.js

...cludes/jquery/plugins/multiple-select/multiple-select.css

...query/plugins/multiple-select/multiple-select.jquery.json

...cludes/jquery/plugins/multiple-select/multiple-select.png

htdocs/includes/jquery/plugins/select2/.gitignore

htdocs/includes/jquery/plugins/select2/CONTRIBUTING.md

htdocs/includes/jquery/plugins/select2/LICENSE

htdocs/includes/jquery/plugins/select2/README.md

htdocs/includes/jquery/plugins/select2/bower.json

htdocs/includes/jquery/plugins/select2/component.json

htdocs/includes/jquery/plugins/select2/composer.json

htdocs/includes/jquery/plugins/select2/package.json

htdocs/includes/jquery/plugins/select2/release.sh

htdocs/includes/jquery/plugins/select2/select2-bootstrap.css

htdocs/includes/jquery/plugins/select2/select2-spinner.gif

htdocs/includes/jquery/plugins/select2/select2.css