Log Message:
tiff: Use only libs_private to express a dependency on liblzma

requires_private assumes the presence of a .pc file, which is not
the case on NetBSD 9.x. This allows builds external from pkgsrc
dependending on libtiff to not fire errors when they fail to find
a corresponding .pc file for liblzma, but still acknowledge the
liblzma dependency.

PR pkg/57539