By default the IdP exposes an HTTP endpoint relative to the deployed servlet context (usually /idp) at /shibboleth which returns the IdP's own metadata. This endpoint path would mirror that implied by the default IdP entityID, for example https://idp.example.org/idp/shibboleth, thereby implementing the Well-Known Location metadata resolution mechanism discussed in the SAML Metadata specification (section 4.1).
That endpoint returns the metadata by simply reading the XML file pointed to by IdP property idp.entityID.metadataFile, the value of which defaults to %{idp.home}/metadata/idp-metadata.xml.
To expose a different metadata file's contents at that endpoint, set that property to a different file path value in conf/idp.properties, for example:
idp.entityID.metadataFile=/var/shibboleth/metadata/idp-metadata.xml
To effectively disable metadata publishing at the endpoint entirely by returning an HTTP 404 response, set the value to an empty string:
idp.entityID.metadataFile=