Clean up unused variable macros.

We might want UNUSED_ASSERTION as a special case but the unused trace
variable macro was being abused in places.

BUG=angleproject:1290

Change-Id: I5f9252b3ff0484d2e859b9fcf68d5d060b28f1fc
Reviewed-on: https://chromium-review.googlesource.com/324290
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/common/debug.cpp b/src/common/debug.cpp
index 466eb6d..1fcc062 100644
--- a/src/common/debug.cpp
+++ b/src/common/debug.cpp
@@ -53,7 +53,7 @@
     }
 
     std::string formattedMessage;
-    UNUSED_TRACE_VARIABLE(formattedMessage);
+    UNUSED_VARIABLE(formattedMessage);
 
 #if !defined(NDEBUG) && defined(_MSC_VER)
     if (messageType == MESSAGE_ERR)