Clean up credential-store-type in schema

    <xsd:complexType name="credential-store-type">
        <xsd:annotation>
            <xsd:documentation>
                An individual credential store definition.
            </xsd:documentation>
        </xsd:annotation>

        <xsd:all minOccurs="0" maxOccurs="1">
            <xsd:element name="attributes" type="attributes-type"/>
            <xsd:element name="protection-parameter-credentials" type="client-credentials-type"/>
            <xsd:element name="providers" type="providers-type" />
        </xsd:all>

        <xsd:attribute name="name" type="xsd:string" use="required" />
        <xsd:attribute name="type" type="xsd:string" default="KeyStoreCredentialStore" use="optional">
            <xsd:annotation>
                <xsd:documentation>
                    The credential store type, e.g. KeyStoreCredentialStore.
                </xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="provider" type="xsd:string" use="optional">
            <xsd:annotation>
                <xsd:documentation>
                    The name of the provider to use to
                    instantiate the CredentialStoreSpi, if the provider is not
                    specified then the first provider found that can
                    create an instance of the specified 'type' will be
                    used.
                </xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
    </xsd:complexType>