This reverts commit f57a4b0ac1.
The old version libtiff_4_5 is no longer needed.
Both dependents (gscan2pdf and hylafaxplus)
have switched to the forked libtiff version 4.6.0t
which is based on the current libtiff version 4.6.0
but also contains required command line tools
missing in the original libtiff library.