cleanup the rushed elastic#3436 PR (elastic#3437)

apm-agent-core/src/test/java/co/elastic/apm/agent/bci/InstrumentationTest.java

@@ -45,6 +45,7 @@
 import org.apache.commons.pool2.impl.CallStackUtils;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.condition.DisabledOnJre;
 import org.junit.jupiter.api.condition.JRE;
@@ -421,8 +422,8 @@ void testPluginClassLoaderGCdAfterUndoingInstrumentation() {
         await().untilAsserted(() -> assertThat(pluginClassLoader.get()).isNull());
     }
 
-    //this is failing from unspecified - likely metaspace specific GC not happening - in CI
-//    @Test
+    @Disabled("this is failing from unspecified - likely metaspace specific GC not happening - in CI")
+    @Test
     void testNoClassLoaderLeakWhenInstrumentedApplicationIsUndeployed() throws Exception {
         ElasticApmAgent.initInstrumentation(tracer,
             ByteBuddyAgent.install(),
@@ -442,10 +443,7 @@ void testNoClassLoaderLeakWhenInstrumentedApplicationIsUndeployed() throws Excep
         applicationCL = null;
         instrumentedClass = null;
 
-        long start = System.currentTimeMillis();
-        while(System.currentTimeMillis()-start < 10_000) {
-
-        }
+        System.gc();
         System.gc();
         await().untilAsserted(() -> assertThat(applicationCLRef.get()).isNull());
     }