Remove wrong javadoc

The heartbeat method doesn't throw GlobalRefDbLockException

Change-Id: I7254b1558eb8cf79794ed9e35f744f43b8374592

src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/Lock.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/Lock.java b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/Lock.java
index 4f2ea21..d65e216 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/Lock.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/spannerrefdb/Lock.java
@@ -184,9 +184,6 @@
    * Update the heartbeat timestamp of the current lock if it matches the expected token. If the
    * tokens do not match, the lock has been reclaimed and a new heartbeat started, so this heartbeat
    * ends.
-   *
-   * @throws GlobalRefDbLockException if the lock unexpectedly no longer exists but the heartbeat is
-   *     still ongoing
    */
   private void heartbeat() {
     try {