RFR: 8318086: [jvmci] RISC-V: Reuse target config from TargetDescription

[Feilong Jiang]

Hi, please review this cleanup. 

[JDK-8262901](https://bugs.openjdk.org/browse/JDK-8262901) moved `linuxOs` and `macOs` from AArch64HotSpotVMConfig.java into TargetDescription.java, we can reuse `linuxOs` for RISC-V.

Testing:

- [x] `compiler/jvmci` with linux-riscv release build

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

Commit messages:
 - remove unused import
 - remove unnecessary linuxOs in RISCV64HotSpotVMConfig.java

Changes: https://git.openjdk.org/jdk/pull/16181/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16181&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318086
  Stats: 5 lines in 2 files changed: 0 ins; 4 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/16181.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16181/head:pull/16181

PR: https://git.openjdk.org/jdk/pull/16181