Deprecate support for Velocity

Support for Velocity has been deprecated in Spring Framework 4.3 with
the plan being to remove it in 5.0. This commit deprecates Spring
Boot's support in 1.4, with the plan being to remove it in 2.0.

Closes gh-5276

spring-boot-samples/spring-boot-sample-velocity/src/test/java/sample/velocity/SampleVelocityApplicationTests.java

@@ -33,6 +33,7 @@ import static org.assertj.core.api.Assertions.assertThat;
  */
 @RunWith(SpringJUnit4ClassRunner.class)
 @SpringApplicationConfiguration(SampleVelocityApplication.class)
+@SuppressWarnings("deprecation")
 public class SampleVelocityApplicationTests {
 
 	@ClassRule