fix(private): remove fallback from flex-direction auto-prefixer

[CaerusKaru]

When we clear styles on the server, we emit an empty value in order to flush the cache. However, all values still end up passing through the auto-prefixer, which then converted this value to the default value of row. However, other components own the default 'row' value fallback, and so this only serves to add another layer of logic that gets in the way. Now, we remove it so that the overlying mechanisms can work as intended in both browser and server.

Fixes #1394

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