Clean up RISC-V RVV performance test files

Removed temporary test files and benchmarks created for omatcopy RVV optimization validation:
- Removed benchmark scripts and result files
- Removed test executables (scalar vs RVV comparison)
- Removed temporary test source files

Previous testing on sg2044 showed RVV implementation achieved ~30% performance improvement
over scalar version for 3000x4000 matrix operations (0.384s vs 0.552s per iteration).

Co-authored-by: gong-flying <gongxiaofei24@iscas.ac.cn>

Author: Dayuxiaoshui