update_engine: remove unused variable

Count is never used in this function.

Test: th
Change-Id: I4987f0268e560eb1a7f5fa9ba9446603dcbf7193
diff --git a/payload_consumer/partition_writer.cc b/payload_consumer/partition_writer.cc
index 2ec05f5..e55722c 100644
--- a/payload_consumer/partition_writer.cc
+++ b/payload_consumer/partition_writer.cc
@@ -190,7 +190,7 @@
   // Setup the ExtentWriter stack based on the operation type.
   std::unique_ptr<ExtentWriter> writer = CreateBaseExtentWriter();
   return install_op_executor_.ExecuteReplaceOperation(
-      operation, std::move(writer), data, count);
+      operation, std::move(writer), data);
 }
 
 bool PartitionWriter::PerformZeroOrDiscardOperation(