...

<xsl:template name="disable_front-page-search" match="dri:div[@id='aspect.discovery.SiteViewer.div.front-page-search']">
</xsl:template>

I'm getting 'relation "bi_5_dis" does not exist' (or any other number)

These are the tables corresponding to individual browse indexes. Browse indexes are defined in dspace.cfg as webui.browse.index.1 through webui.browse.index.n and you can modify which metadata fields you want in the indexes, but you have to remember that after any such change, you need to re-create the indexes.

See ReIndexing Content (for Browse or Search) in the official documentation for your version of DSpace.

See also the relevant dspace.cfg section.