tests: fix a copy/paste name duplication in storage.py
Flagged by PyCharm as a redeclared name without usage, because the name matches
the function immediately preceding it. But since this differs by doing regular
reads instead of raw reads, I assume we still want it. But I don't see either
function being called anywhere.
Differential Revision: https://phab.mercurial-scm.org/D7769
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