[riscv-port-jdk17u:riscv-port] RFR: 8291893: riscv: remove fence.i used in user space [v2]

[Dingli Zhang]

> Please review this backport to riscv-port-jdk17u.
> Backport of [JDK-8291893](https://bugs.openjdk.org/browse/JDK-8291893).
> 
> The original patch cannot be directly applied because of the line number, but there are no other additional changes.
> 
> Testing:
> - Tier1 passed without new failure on unmacthed (release).

Dingli Zhang has updated the pull request incrementally with one additional commit since the last revision:

  rebase

-------------

Changes:
  - all: https://git.openjdk.org/riscv-port-jdk17u/pull/13/files
  - new: https://git.openjdk.org/riscv-port-jdk17u/pull/13/files/0bec4f0a..31aee659

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=13&range=01
 - incr: https://webrevs.openjdk.org/?repo=riscv-port-jdk17u&pr=13&range=00-01

  Stats: 9 lines in 1 file changed: 0 ins; 8 del; 1 mod
  Patch: https://git.openjdk.org/riscv-port-jdk17u/pull/13.diff
  Fetch: git fetch https://git.openjdk.org/riscv-port-jdk17u pull/13/head:pull/13

PR: https://git.openjdk.org/riscv-port-jdk17u/pull/13