Simplify the Actuator's hypermedia support

This commit replaces the Acuator's support for hypermedia with a
single endpoint that returns HAL-formatted links to all of the
available endpoints. This is done without requiring Spring HATEOAS
to be on the classpath in a similar manner to the existing
CloudFoundry discovery endpoint.

Closes gh-9901

Author: wilkinsona

Diff for: spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/EndpointWebMvcHypermediaManagementContextConfiguration.java

@@ -29,6 +29,7 @@
 import org.springframework.boot.actuate.endpoint.Endpoint;
 import org.springframework.boot.actuate.endpoint.mvc.EndpointHandlerMapping;
 import org.springframework.boot.actuate.endpoint.mvc.MvcEndpoint;
+import org.springframework.boot.actuate.endpoint.mvc.NamedMvcEndpoint;
 import org.springframework.boot.autoconfigure.AutoConfigureAfter;
 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
@@ -379,7 +380,7 @@ private EndpointHandlerMapping getRequiredEndpointHandlerMapping() {
 			if (endpointHandlerMapping == null) {
 				// Maybe there are actually no endpoints (e.g. management.port=-1)
 				endpointHandlerMapping = new EndpointHandlerMapping(
-						Collections.<MvcEndpoint>emptySet());
+						Collections.<NamedMvcEndpoint>emptySet());
 			}
 			return endpointHandlerMapping;
 		}

Diff for: spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/ManagementWebSecurityAutoConfiguration.java

@@ -21,7 +21,6 @@
 
 import org.springframework.boot.actuate.endpoint.Endpoint;
 import org.springframework.boot.actuate.endpoint.mvc.AbstractEndpointHandlerMapping;
-import org.springframework.boot.actuate.endpoint.mvc.HalJsonMvcEndpoint;
 import org.springframework.boot.actuate.endpoint.mvc.HealthMvcEndpoint;
 import org.springframework.boot.actuate.endpoint.mvc.MvcEndpoint;
 import org.springframework.boot.actuate.endpoint.mvc.NamedMvcEndpoint;
@@ -50,10 +49,7 @@ protected void postProcessEndpoints(Set<NamedMvcEndpoint> endpoints) {
 		HealthMvcEndpoint healthMvcEndpoint = null;
 		while (iterator.hasNext()) {
 			NamedMvcEndpoint endpoint = iterator.next();
-			if (endpoint instanceof HalJsonMvcEndpoint) {
-				iterator.remove();
-			}
-			else if (endpoint instanceof HealthMvcEndpoint) {
+			if (endpoint instanceof HealthMvcEndpoint) {
 				iterator.remove();
 				healthMvcEndpoint = (HealthMvcEndpoint) endpoint;
 			}