Remove included file string_util.h from payload_signer.cc am: a9a2513870

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3309435

Change-Id: I357653cb4578252669f8d86aed883aeff3969f44
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>
diff --git a/payload_generator/payload_signer.cc b/payload_generator/payload_signer.cc
index 4b24eba..b661a92 100644
--- a/payload_generator/payload_signer.cc
+++ b/payload_generator/payload_signer.cc
@@ -23,7 +23,6 @@
 
 #include <base/logging.h>
 #include <base/strings/string_number_conversions.h>
-#include <base/strings/string_util.h>
 #include <brillo/data_encoding.h>
 #include <openssl/err.h>
 #include <openssl/pem.h>