Remove included file string_split.h from payload_signer.cc am: 4e1be09cc6

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/3304585

Change-Id: I34b9094309061c16eada980bbc67aad3dedbea9d
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 11e136f..4b24eba 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_split.h>
 #include <base/strings/string_util.h>
 #include <brillo/data_encoding.h>
 #include <openssl/err.h>