Remove fomantic ".link" selector and styles (#23888)
It's difficult to play with Fomantic's ".link" selector&styles, and it
doesn't bring any real benefit.
Instead, it sometimes introduces regressions (because of the `:not`
selector, really difficult to fine-tune).
Regression:
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After this PR, there is no ".link" in code anymore. We do not need to
play the overwriting and `:not()` game anymore.
