Don't do a strict taxonomy check in `get_category_link()`.

Prior to version 4.9, a quirk in the implementation of `get_term()` caused
`get_category_link( 123 )` to fetch the taxonomy archive link for term 123
even if 123 is not in the 'category' taxonomy. The quirk was fixed in [40979];
see #40671. This bugfix introduced a regression for theme authors who were
expecting the old behavior.

By lifting the 'category' restriction, we allow the template function to work
in the old way.

Fixes #42717. See #42771.
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