The attached patch makes it possible to make some links not
descriptively if a variable for the link is defined and its value is not
'org-link.

There are a few scenarios where this would be good. In org-ref I apply
an advice to the activate-bracket-link function to undo the descriptive
link showing for cite links which use the description for additional
information like page numbers.

Another use that inspired this is a set of commenting links that might
look like: [[replace:JK some old text][some new text]] where it might be
desirable to see the whole link, but keep other descriptive links in the
descriptive form.

Thoughts?