wp-embedded-content

Nope, the hidden iframe is part of WordPress Embed Post.

Here's blockquote html:

<blockquote class="wp-embedded-content" data-secret="by9Rs75NEz"><p><a href="http://canacochihuahua.com/encuesta/medios-electronicos-2/"><font style="vertical-align: inherit;"><font style="vertical-align: inherit;">Electronic media</font></font></a></p></blockquote>

and here's iframe:

<iframe class="wp-embedded-content" sandbox="allow-scripts" security="restricted" style="position: absolute; clip: rect(1px, 1px, 1px, 1px);" src="https://canacochihuahua.com/encuesta/medios-electronicos-2/embed/#?secret=by9Rs75NEz" data-secret="by9Rs75NEz" width="600" height="338" title="&quot;Electronic Media&quot; - CANACO" frameborder="0" marginwidth="0" marginheight="0" scrolling="no"></iframe>

As you can see, they share some common data. Without that hidden iframe, the blockquote is just a normal blockquote, not WordPress Embed Post anymore.

According to the updated checklist https://instantview.telegram.org/checklist#6-4-4-popular-widgets:

Telegram is likely to support the following popular widgets in the future:

• WordPress Embed Post

Supporting content from these widgets is optional since it will eventually become available through official means.

So, you'd better leave it as it is.