Fixes duplicated table creation when running the application

The double persistence.xml in JSF and REST projects was causing
problems in some environments, as the tables were created twice.

This commit fixes this error by moving the persistence.xml to the
service layer.

rest/src/main/resources/META-INF/persistence.xml

-<?xml version="1.0" encoding="UTF-8"?>
-<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
-  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-  xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
-             http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
-  version="2.1">
-  <persistence-unit name="runtime">
-    <jta-data-source>java:jboss/datasources/xcs</jta-data-source>
-
-    <class>es.uvigo.esei.xcs.domain.entities.Owner</class>
-    <class>es.uvigo.esei.xcs.domain.entities.Pet</class>
-    <class>es.uvigo.esei.xcs.domain.entities.Administrator</class>
-    <exclude-unlisted-classes>false</exclude-unlisted-classes>
-
-    <properties>
-      <property name="hibernate.hbm2ddl.auto" value="update" />
-      <property name="hibernate.show_sql" value="false" />
-    </properties>
-  </persistence-unit>
-</persistence>
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