Simplify span end time.

The only reason to have now() returned in getEndEpochNanos seems to be
that it kinda makes sense for getLatencyMs, but that method is
package-private and never used.

See also
open-telemetry/opentelemetry-specification#373 (comment).

sdk/src/main/java/io/opentelemetry/sdk/trace/RecordEventsReadableSpan.java

@@ -220,14 +220,14 @@ public InstrumentationLibraryInfo getInstrumentationLibraryInfo() {
   }
 
   /**
-   * Returns the end nano time (see {@link System#nanoTime()}). If the current {@code Span} is not
-   * ended then returns {@link Clock#nanoTime()}.
+   * Returns the end nano time (see {@link System#nanoTime()}) or zero if the current {@code Span}
+   * is not ended.
    *
    * @return the end nano time.
    */
   private long getEndEpochNanos() {
     synchronized (lock) {
-      return getEndNanoTimeInternal();
+      return endEpochNanos;
     }
   }
 
@@ -291,24 +291,6 @@ Map<String, AttributeValue> getAttributes() {
     }
   }
 
-  /**
-   * Returns the latency of the {@code Span} in nanos. If still active then returns now() - start
-   * time.
-   *
-   * @return the latency of the {@code Span} in nanos.
-   */
-  long getLatencyNs() {
-    synchronized (lock) {
-      return getEndNanoTimeInternal() - startEpochNanos;
-    }
-  }
-
-  // Use getEndNanoTimeInternal to avoid over-locking.
-  @GuardedBy("lock")
-  private long getEndNanoTimeInternal() {
-    return hasBeenEnded ? endEpochNanos : clock.now();
-  }
-
   /**
    * Returns the kind of this {@code Span}.
    *

sdk/src/test/java/io/opentelemetry/sdk/trace/RecordEventsReadableSpanTest.java

@@ -134,7 +134,7 @@ public void toSpanData_ActiveSpan() {
           Collections.singletonList(link),
           SPAN_NEW_NAME,
           startEpochNanos,
-          testClock.now(),
+          0,
           Status.OK);
     } finally {
       span.end();
@@ -243,32 +243,6 @@ public void getAndUpdateSpanName() {
     }
   }
 
-  @Test
-  public void getLatencyNs_ActiveSpan() {
-    RecordEventsReadableSpan span = createTestSpan(Kind.INTERNAL);
-    try {
-      testClock.advanceMillis(MILLIS_PER_SECOND);
-      long elapsedTimeNanos1 = testClock.now() - startEpochNanos;
-      assertThat(span.getLatencyNs()).isEqualTo(elapsedTimeNanos1);
-      testClock.advanceMillis(MILLIS_PER_SECOND);
-      long elapsedTimeNanos2 = testClock.now() - startEpochNanos;
-      assertThat(span.getLatencyNs()).isEqualTo(elapsedTimeNanos2);
-    } finally {
-      span.end();
-    }
-  }
-
-  @Test
-  public void getLatencyNs_EndedSpan() {
-    RecordEventsReadableSpan span = createTestSpan(Kind.INTERNAL);
-    testClock.advanceMillis(MILLIS_PER_SECOND);
-    span.end();
-    long elapsedTimeNanos = testClock.now() - startEpochNanos;
-    assertThat(span.getLatencyNs()).isEqualTo(elapsedTimeNanos);
-    testClock.advanceMillis(MILLIS_PER_SECOND);
-    assertThat(span.getLatencyNs()).isEqualTo(elapsedTimeNanos);
-  }
-
   @Test
   public void setAttribute() {
     RecordEventsReadableSpan span = createTestRootSpan();