table: silence unused variable warning in release builds

Warning introduced in commit 80f9fcdaa17aa9acf322e6bca34b41cc57415ad7

refs #3164

Change-Id: I3e97a1f6adf3beedc4b5608cac75a276735891cb
diff --git a/daemon/table/measurements.cpp b/daemon/table/measurements.cpp
index 60011e2..3830c10 100644
--- a/daemon/table/measurements.cpp
+++ b/daemon/table/measurements.cpp
@@ -127,8 +127,7 @@
 void
 Measurements::extendLifetime(Entry& entry, const time::nanoseconds& lifetime)
 {
-  name_tree::Entry* nte = m_nameTree.getEntry(entry);
-  BOOST_ASSERT(nte != nullptr);
+  BOOST_ASSERT(m_nameTree.getEntry(entry) != nullptr);
 
   time::steady_clock::TimePoint expiry = time::steady_clock::now() + lifetime;
   if (entry.m_expiry >= expiry) {