Remove excessive stores from the error estimation mode

[PetroZarytskyi]

In the error estimation mode, we create _EERepl_ variables, which are used to store the values of variables at every point of the function to then use them in the reverse sweep. However, on the current master, we can simply use the original variables instead since we now restore their values in the reverse sweep. We don't have to store any intermediate values in error estimation now.