Remove Java security context serialization (#2677)

Remove Java security context serialization - it is replaced by JSON security context serialization (optimized as size). Backward incompatible change.
Java security context serialization was not used in default hawkbit runtime out of the box. So, it's assumed none uses it. 
Anyway, if anyone has enabled it, he could, in order to keep backward compatibility, get the java security context serialization from the previous hawkbit releases/commits and register it again as a spring bean in his hawkbit extension.

Signed-off-by: Avgustin Marinov <Avgustin.Marinov@bosch.com>

hawkbit-repository/hawkbit-repository-test/src/main/java/org/eclipse/hawkbit/repository/test/TestConfiguration.java

@@ -47,6 +47,7 @@ import org.eclipse.hawkbit.tenancy.configuration.ControllerPollProperties;
 import org.eclipse.hawkbit.tenancy.configuration.TenantConfigurationProperties;
 import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
 import org.springframework.aop.interceptor.SimpleAsyncUncaughtExceptionHandler;
+import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.cache.caffeine.CaffeineCacheManager;
@@ -144,11 +145,6 @@ public class TestConfiguration implements AsyncConfigurer {
         return (tenant, username) -> Collections.emptyList();
     }
 
-    @Bean
-    SecurityContextSerializer securityContextSerializer() {
-        return SecurityContextSerializer.JSON_SERIALIZATION;
-    }
-
     @Bean
     TenantResolver tenantResolver() {
         return new DefaultTenantResolver();
@@ -156,7 +152,8 @@ public class TestConfiguration implements AsyncConfigurer {
 
     @Bean
     ContextAware contextAware(
-            final UserAuthoritiesResolver authoritiesResolver, final SecurityContextSerializer securityContextSerializer,
+            final UserAuthoritiesResolver authoritiesResolver,
+            @Autowired(required = false) final SecurityContextSerializer securityContextSerializer,
             final TenantResolver tenantResolver) {
         // allow spying the security context
         return org.mockito.Mockito.spy(new SecurityContextTenantAware(authoritiesResolver, securityContextSerializer, tenantResolver));