Prefer "similar" over "equivalent" in tutorial (#125343)

In the datastructures tutorial doc, some operations are described as
"equivalent to" others. This has led to some user-confusion -- at
least in the Discourse forums -- about cases in which the operations
differ.

This change doesn't systematically eliminate the word "equivalent"
from the tutorial. It just substitutes "similar to" in several cases
in which "equivalent to" could mislead users into expecting exact
equivalence.