Name of writing style which avoids both first/second/third person

What is the name of the style of writing, often seen in technical manuals and documentation, which avoids using the first, second or third person.

For example, if I were writing a manual on making a cup of tea, I would avoid both of the following

I tend to pour the water first, then remove the teabag and add milk.

and

You should pour the water first, then you should remove the teabag and add the milk.

In favour of the style:

The water should be poured over the teabag, removed, and then the milk should be added.

I am trying to write guidelines on using a specific writing style, but I do not know what to call this style of writing.

_{*For tea purists, I know it should be drunk without milk, as nature intended!}