docs: animations - replace iterator with simple code style

[wardbell]

Replaces iterator facade over the HeroService because webpack threw up.
Also this was an obscure distraction for readers with no obvious benefits.
This is a pure refactor (with prose). The examples should behave exactly as before.

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PR Type

What kind of change does this PR introduce?

[x] Bugfix (fixed by the refactor)
[ ] Feature
[ ] Code style update (formatting, local variables)
[x] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[x] Documentation content changes
[ ] angular.io application / infrastructure changes
[ ] Other... Please describe:

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[Foxandxss]

One petition @wardbell. In the big template file where all other components are loaded, there are a few [heroes]=heroes. Notice, no quotes. Can you add them?

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