RFR: 8330095: RISC-V: Remove obsolete vandn_vi instruction

[Gui Cao]

Hi, We notice that the `vandn_vi` instruction is defined in the current code and is not used anywhere, it is not available in the riscv-crypto Release-1.0.0 manual. The `vandn_vi` instruction is present in earlier riscv-crypto manual, but the `vandnvi` has been removed from the https://github.com/riscv/riscv-crypto/commit/82a02f09668adb18dfee5dfc45a0ce7d3af10103 commit.

### Testing
- [x]  fastdebug build successfully

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Commit messages:
 - RISC-V: Remove obsolete vandn_vi instruction

Changes: https://git.openjdk.org/jdk/pull/18737/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18737&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330095
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18737.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18737/head:pull/18737

PR: https://git.openjdk.org/jdk/pull/18737