[RISCV] Remove -riscv-v-vector-bits-min in tests. NFC (#65404)

V implies Zvl128b, but a lot of the fixed vector tests also redundantly
specify -riscv-v-vector-bits-min=128. This patch removes them where
there isn't another minimum vlen being tested for, and for cases where
Zve* is being used Zvl128b was added to maintain the old test diff (and
because an awkward vlen probably isn't interesting to test for). Other
places where -risc-v-vector-bits-min were being used were replaced with
Zvl.