[llvm] [nfc][InstrProf]Remove 'offsetOf' when parsing indexed profiles (PR #93346)

[Mingming Liu via llvm-commits]

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@@ -1704,19 +1685,17 @@ size_t Header::size() const {
                   "been added to the header, if not add a case statement to "
                   "fall through to the latest version.");
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minglotus-6 wrote:

done. I also updated the assert message in `static_assert(std::is_standard_layout_v<Header>`.

https://github.com/llvm/llvm-project/pull/93346