hylafaxplus: switch to current libtiff 4.6.0t

hylafaxplus is not compatible with libtiff 4.6.0
as published on https://libtiff.gitlab.io/libtiff/
and http://www.simplesystems.org/libtiff/ .
To fix the build, we used an older libtiff version
(see cd3771c709).

In the meantime, hylafaxplus developer Lee Howard
published a forked version "4.6.0t" of libtiff,
providing the missing tools for hylafaxplus, see
https://sourceforge.net/p/hylafax/mailman/message/58751879/ .
The commit at hand changes the libtiff
version for hylafaxplus to use that fork.

pkgs/top-level/all-packages.nix

@@ -9167,8 +9167,9 @@ with pkgs;
   hybridreverb2 = callPackage ../applications/audio/hybridreverb2 { };
 
   hylafaxplus = callPackage ../servers/hylafaxplus {
-    # libtiff >= 4.6 dropped many executables needed by hylafaxplus
-    libtiff = libtiff_4_5;
+    # needs this fork of libtiff, because original libtiff
+    # stopped packaging required tools with version 4.6
+    libtiff = libtiff_t;
   };
 
   hyphen = callPackage ../development/libraries/hyphen { };