Remove old unused code (#8343)

Author: jbachorik

dd-java-agent/agent-profiling/profiling-controller/src/main/java/com/datadog/profiling/controller/ProfilingSystem.java

@@ -19,7 +19,6 @@
 import static datadog.trace.util.AgentThreadFactory.AgentThread.PROFILER_RECORDING_SCHEDULER;
 
 import datadog.trace.api.Platform;
-import datadog.trace.api.profiling.ProfilingListenersRegistry;
 import datadog.trace.api.profiling.ProfilingSnapshot;
 import datadog.trace.api.profiling.RecordingData;
 import datadog.trace.api.profiling.RecordingDataListener;
@@ -265,7 +264,6 @@ public void snapshot(boolean onShutdown) {
             recording.snapshot(
                 lastSnapshot,
                 onShutdown ? ProfilingSnapshot.Kind.ON_SHUTDOWN : ProfilingSnapshot.Kind.PERIODIC);
-        ProfilingListenersRegistry.getHost(ProfilingSnapshot.class).fireOnData(recordingData);
         log.debug("Snapshot created: {}", recordingData);
         if (recordingData != null) {
           // To make sure that we don't get data twice, we say that the next start should be

dd-trace-core/src/main/java/datadog/trace/core/DDSpan.java

@@ -19,7 +19,6 @@
 import datadog.trace.api.gateway.RequestContext;
 import datadog.trace.api.metrics.SpanMetricRegistry;
 import datadog.trace.api.metrics.SpanMetrics;
-import datadog.trace.api.profiling.TransientProfilingContextHolder;
 import datadog.trace.api.sampling.PrioritySampling;
 import datadog.trace.api.sampling.SamplingMechanism;
 import datadog.trace.bootstrap.debugger.DebuggerContext;
@@ -48,12 +47,9 @@
  * <p>Spans are created by the {@link CoreTracer#buildSpan}. This implementation adds some features
  * according to the DD agent.
  */
-public class DDSpan
-    implements AgentSpan, CoreSpan<DDSpan>, TransientProfilingContextHolder, AttachableWrapper {
+public class DDSpan implements AgentSpan, CoreSpan<DDSpan>, AttachableWrapper {
   private static final Logger log = LoggerFactory.getLogger(DDSpan.class);
 
-  public static final String CHECKPOINTED_TAG = "checkpointed";
-
   static DDSpan create(
       final String instrumentationName,
       final long timestampMicro,

internal-api/src/main/java/datadog/trace/api/profiling/ObservableType.java

@@ -1,6 +1,6 @@
 package datadog.trace.api.profiling;
 
-public interface ProfilingSnapshot extends ObservableType {
+public interface ProfilingSnapshot {
   enum Kind {
     PERIODIC,
     ON_SHUTDOWN