Fix mixing string references in Motion Blinds translations

[starkillerOG]

Breaking change

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Process late feedback from @MartinHjelmare for this PR: #68589 (review)

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[starkillerOG]

@MartinHjelmare I resolved the mixing of string refrences with regular text in this PR, as you requested.

[frenck]

We can just use:

[%key:common::config_flow::abort::already_configured_device%]

As that is the default / common abort message we use across all integration.

[starkillerOG]

I changed it to only the string refrence.