simplify GEMM call path: remove unused APIs from gemm.hpp
simplify GEMM call path: remove unused APIs from gemm.hpp

ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen,ROCmSoftwarePlatform/MIOpen