[riscv64-8u]drop shenandoah

[sendaoYan]

> git status
On branch minus-jbs8276799
Changes not staged for commit:
  (use "git add/rm <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   hotspot/src/cpu/riscv/vm/c1_LIRAssembler_riscv.cpp
        deleted:    hotspot/src/cpu/riscv/vm/gc/shenandoah/c1/shenandoahBarrierSetC1_riscv.cpp
        deleted:    hotspot/src/cpu/riscv/vm/gc/shenandoah/shenandoahBarrierSetAssembler_riscv.cpp
        deleted:    hotspot/src/cpu/riscv/vm/gc/shenandoah/shenandoahBarrierSetAssembler_riscv.hpp
        deleted:    hotspot/src/cpu/riscv/vm/gc/shenandoah/shenandoah_riscv64.ad
        modified:   hotspot/src/cpu/riscv/vm/riscv.ad
        modified:   hotspot/src/cpu/riscv/vm/templateInterpreterGenerator_riscv.cpp

[sendaoYan]

make-x86_64.log make-aarch64.log make-riscv64.log