maven: Use BeautifulSoup instead of xmltodict for parsing pom files
xmltodict cannot parse POM files with multi-byte encoding so prefer to use the XML parser of BeautifulSoup based on lxml instead.
Also drop xmltodict requirement as it is no longer used in swh-lister codebase.
Fixes SWH-LISTER-69
Migrated from D8217 (view on Phabricator)