Revert "fix cuda half math function is undefined: hpow, htanh (apache…

…#6225)" (apache#6249)

This reverts commit ed04cdd.

src/target/source/literal/cuda_half_t.h

@@ -293,19 +293,6 @@ __pack_half2(const half x, const half y) {
   unsigned v1 = *((unsigned short *)&y);
   return (v1 << 16) | v0;
 }
-
-static inline __device__ __host__ half hpow(half x, half y) {
-  float tmp_x = __half2float(x);
-  float tmp_y = __half2float(y);
-  float result = powf(tmp_x, tmp_y);
-  return __float2half(result);
-}
-
-static inline __device__ __host__ half htanh(half x) {
-  float tmp_x = __half2float(x);
-  float result = tanhf(tmp_x);
-  return __float2half(result);
-}
 )";
 
 static constexpr const char* _cuda_warp_intrinsic_util = R"(