fd/managed: Remove unused header

Change-Id: I64515757dce6391a6c1d78acb66b7ba5e130c5c8
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/src/fd/managed.cpp b/src/fd/managed.cpp
index cd4ec1c..5669903 100644
--- a/src/fd/managed.cpp
+++ b/src/fd/managed.cpp
@@ -1,4 +1,3 @@
-#include <fmt/format.h>
 #include <unistd.h>
 
 #include <stdplus/fd/dupable.hpp>