scrolledwindow: Remove redundant use of MAX

scrolledwindow: Remove redundant use of MAX

This code tries to add the minimum content size, if one is set, to the
GtkScrolledWindow's size requisition. This is obvious from the check
for non-negative values of min-content-height and min-content-width.
Using MAX needlessly makes the code harder to read by implying that
there is more to it when there actually isn't.

Fall out from 0d9ebb501df60cf1803858efcd1c79542588abd8

https://bugzilla.gnome.org/show_bug.cgi?id=766569