[llvm] [RISCV] Remove -riscv-v-fixed-length-vector-lmul-max from arith tests (PR #89886)

[Luke Lau via llvm-commits]

https://github.com/lukel97 approved this pull request.

LGTM. We can probably also remove it from the other tests in test/Analysis/CostModel/RISCV

https://github.com/llvm/llvm-project/pull/89886