riscv: Get rid of some unused constants.
riscv: Get rid of some unused constants.

Change-Id: I464e86dc6bfcd333a0bee32e56d9dcaa6fdf682d
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39317
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Ayaz Akram <b0ec8a52890ea7143b5fcee752bd38bab0d9ccae@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>

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