DATACMNS-571 - Remove custom build infrastructure for Optional.

We now require a JDK to build Spring Data Commons as using the custom Optional type from the Spring Data Build project as it causes the tests to break as Spring 4.1 snapshots load the Optional type to check for it's ability on the classpath which the JVM rejects.

pom.xml

@@ -128,13 +128,6 @@
 			<optional>true</optional>
 		</dependency>
 
-		<dependency>
-			<groupId>org.springframework.data.build</groupId>
-			<artifactId>spring-data-java8-stub</artifactId>
-			<version>1.5.0.RC1</version>
-			<scope>provided</scope>
-		</dependency>
-
 		<dependency>
 			<groupId>javax.el</groupId>
 			<artifactId>el-api</artifactId>
@@ -220,7 +213,7 @@
 				<configuration>
 					<rules>
 						<requireJavaVersion>
-							<version>[1.7,1.9)</version>
+							<version>[1.8,1.9)</version>
 						</requireJavaVersion>
 					</rules>
 				</configuration>