Fix Guacamole Docker Documentation to indiciate image does not support LDAP Docker Links

Fix Guacamole Docker Documentation to indiciate image does not support Docker Links.

The documentation which is published at https://guacamole.apache.org/doc/gug/guacamole-docker.html#guacamole-docker-ldap states

To use Guacamole with the LDAP authentication backend, you will need network access to an LDAP directory. Unlike MySQL and PostgreSQL, the Guacamole Docker image does support Docker links for LDAP; the connection information must be specified using environment variables:

This should be (without the added emphasis)

To use Guacamole with the LDAP authentication backend, you will need network access to an LDAP directory. Unlike MySQL and PostgreSQL, the Guacamole Docker image does not support Docker links for LDAP; the connection information must be specified using environment variables: