Fixes #4309 - flickr shortcode: size parameter not used anywhere

[bobbingwide]

Fixes #4309 .

Changes proposed in this Pull Request:

Delete the line containing the only instance of 'size'

I don't see the need to change any test cases.

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[enejb]

This make sense to me.
I don't think we ever implemented the size parameter.

[enejb]

This PR needs to be rebased in order for us to merge it.