scripted-diff: Use std::span over Span

-BEGIN VERIFY SCRIPT-

 ren() { sed -i "s!\<$1\>!$2!g" $( git grep -l "$1" -- "./src" ":(exclude)src/span.h" ":(exclude)src/leveldb/db/log_test.cc" ) ; }

 ren Span            std::span
 ren AsBytes         std::as_bytes
 ren AsWritableBytes std::as_writable_bytes

 sed -i 's!SpanPopBack(Span!SpanPopBack(std::span!g' ./src/span.h

-END VERIFY SCRIPT-

src/span.h

@@ -73,7 +73,7 @@
 
 /** Pop the last element off a span, and return a reference to that element. */
 template <typename T>
-T& SpanPopBack(Span<T>& span)
+T& SpanPopBack(std::span<T>& span)
 {
     size_t size = span.size();
     T& back = span.back();