doc: remove buffered flag from performance hooks examples

The actual implementation of the observe method does not count the buffered flag if we use the entryTypes with it. Therefore, examples with both entryTypes and buffered are confusing because it doesn't have any effect on the actual behaviour.

I see that we have somewhat similar PR on the same topic. However, it doesn't provide changes to the examples. Also, I'm not sure at what stage the PR I linked is. If it stuck and not going anywhere I can work on it and deliver the whole fix instead of just examples.