Remove redunant method

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/TraceCallable.java

@@ -48,7 +48,7 @@ public class TraceCallable<V> extends TraceDelegate<Callable<V>> implements Call
 			return this.getDelegate().call();
 		}
 		finally {
-			closeAll(span);
+			close(span);
 		}
 	}
 

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/TraceDelegate.java

@@ -48,10 +48,6 @@ public abstract class TraceDelegate<T> {
 		this.tracer.close(span);
 	}
 
-	protected void closeAll(Span span) {
-		span = this.tracer.close(span);
-	}
-
 	protected Span startSpan() {
 		return this.tracer.joinTrace(getSpanName(), this.parent);
 	}

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/TraceRunnable.java

@@ -45,7 +45,7 @@ public class TraceRunnable extends TraceDelegate<Runnable> implements Runnable {
 			this.getDelegate().run();
 		}
 		finally {
-			closeAll(span);
+			close(span);
 		}
 	}
 }

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/DefaultTracer.java

@@ -134,7 +134,7 @@ public class DefaultTracer implements Tracer {
 			return span;
 		}
 		else {
-			if (SpanContextHolder.getCurrentSpan() == null) {
+			if (!isTracing()) {
 				SpanContextHolder.push(parent, true);
 			}
 			Span span = Span.builder().begin(System.currentTimeMillis()).name(name)