The eXist database is no longer included in the standard Orbeon Forms WAR file. If you are using that version or newer, you don't need to explicitly remove eXist.
Rationale
By default, Orbeon Forms ships with an embedded eXist-db database. For production, this is not an ideal setup and it is better to have a separate eXist-db database. After you download and install eXist-db, you should follow the instruction below to set it up, and let Orbeon Forms know how it should connect to eXist-db.
Setup
Configuring full-text indexing in eXist-db
Orbeon Forms uses the Lucene-based full-text index. Without this configuration, free-text search in the Form Runner Summary page won't work. After you install eXist-db, store a collection.xconf file as follows in the eXist-db, under system/config/db/orbeon/fr/. You can also find the latest version of this file on GitHub.
<collectionxmlns="http://exist-db.org/collection-config/1.0"><index><!-- Disable the standard full text index --><fulltextdefault="none"attributes="no"/><!-- Lucene index is configured below --><lucene><analyzerclass="org.apache.lucene.analysis.standard.StandardAnalyzer"/><!-- We want to index the content of all form elements --><textmatch="//*"/></lucene></index></collection>
Configuring Form Runner
Set the oxf.fr.persistence.exist.exist-uri in your Orbeon Forms properties-local.xml to tell Form Runner how to connect to your eXist-db REST API, using the appropriate URL.