RFR: 8339237: RISC-V: Builds fail after JDK-8339120

[duke]

On Thu, 29 Aug 2024 10:56:01 GMT, Gui Cao <gcao at openjdk.org> wrote:

> Encountered this build warning/error when doing a native build on linux-riscv64 platform with GCC-13. We can simply remove float_regs_as_doubles_size_in_slots in file c1_Runtime1_riscv.cpp as it is not used anywhere.
> 
> ### Testing
> - [x] release & fastdebug build OK on linux-riscv64 after this change.

@zifeihan 
Your change (at version edadbddf3ee653eebec4d63cbe0dbc78638f1108) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/20765#issuecomment-2317824436