Removed unused includes

The clangd LSP indicates when includes aren't used directly.

Tested:
Unit tests pass

Change-Id: I0306be1439317ff40981a8bf221ea7d8a652e281
Signed-off-by: Matt Spinler <spinler@us.ibm.com>
diff --git a/util.cpp b/util.cpp
index 3847e0a..7ef2d44 100644
--- a/util.cpp
+++ b/util.cpp
@@ -27,6 +27,7 @@
 #include <sdbusplus/bus.hpp>
 
 #include <chrono>
+#include <fstream>
 
 namespace phosphor::logging::util
 {