fix unused variables (PaddlePaddle#76744)

Author: co63oc

paddle/phi/infermeta/binary.cc

@@ -1882,7 +1882,6 @@ void FastRMSNormInfermeta(const MetaTensor& x,
                         "0.0 and 0.001, But received [%s].",
                         epsilon));
 
-  phi::DataType x_dtype = x.dtype();
   phi::DataType scale_dtype = scale.dtype();
   y->set_dims(x_dim);
   y->set_dtype(scale_dtype);

paddle/phi/infermeta/ternary.cc

@@ -666,7 +666,6 @@ void FastLayerNormInfermeta(const MetaTensor& x,
                         "0.0 and 0.001, But received [%s].",
                         epsilon));
 
-  phi::DataType x_dtype = x.dtype();
   phi::DataType scale_dtype = scale.dtype();
   y->set_dims(x_dim);
   y->set_dtype(scale_dtype);