Remove #include <span> (#10535)

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@diff-train-skip-merge

Co-authored-by: lucylq <[email protected]>

Author: pytorchbot

runtime/core/test/span_test.cpp

@@ -7,7 +7,6 @@
  */
 
 #include <executorch/runtime/core/span.h>
-#include <span>
 
 #include <gtest/gtest.h>