Cleanup: removing unused class (elastic#34541) (elastic#34571)

Backport of elastic#34541. Original description:

This PR just removes the `USER_INFO` class constants that aren't actually being used anywhere. Once these are removed, there is also need for their type to exist, the class `BuiltinUserInfo`, so this PR removes this class as well.

Author: ycombinator

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/APMSystemUser.java

@@ -16,7 +16,6 @@ public class APMSystemUser extends User {
     public static final String NAME = UsernamesField.APM_NAME;
     public static final String ROLE_NAME = UsernamesField.APM_ROLE;
     public static final Version DEFINED_SINCE = Version.V_6_5_0;
-    public static final BuiltinUserInfo USER_INFO = new BuiltinUserInfo(NAME, ROLE_NAME, DEFINED_SINCE);
 
     public APMSystemUser(boolean enabled) {
         super(NAME, new String[]{ ROLE_NAME }, null, null, MetadataUtils.DEFAULT_RESERVED_METADATA, enabled);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/BeatsSystemUser.java

@@ -16,7 +16,6 @@ public class BeatsSystemUser extends User {
     public static final String NAME = UsernamesField.BEATS_NAME;
     public static final String ROLE_NAME = UsernamesField.BEATS_ROLE;
     public static final Version DEFINED_SINCE = Version.V_6_3_0;
-    public static final BuiltinUserInfo USER_INFO = new BuiltinUserInfo(NAME, ROLE_NAME, DEFINED_SINCE);
 
     public BeatsSystemUser(boolean enabled) {
         super(NAME, new String[]{ ROLE_NAME }, null, null, MetadataUtils.DEFAULT_RESERVED_METADATA, enabled);

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/security/user/BuiltinUserInfo.java

@@ -16,7 +16,6 @@ public class LogstashSystemUser extends User {
     public static final String NAME = UsernamesField.LOGSTASH_NAME;
     public static final String ROLE_NAME = UsernamesField.LOGSTASH_ROLE;
     public static final Version DEFINED_SINCE = Version.V_5_2_0;
-    public static final BuiltinUserInfo USER_INFO = new BuiltinUserInfo(NAME, ROLE_NAME, DEFINED_SINCE);
 
     public LogstashSystemUser(boolean enabled) {
         super(NAME, new String[]{ ROLE_NAME }, null, null, MetadataUtils.DEFAULT_RESERVED_METADATA, enabled);