[backend] remove Types::Serialiser reference

It's no longer needed for newer JSON::XS versions.

src/backend/bs_notar

@@ -24,18 +24,10 @@
 BEGIN {
   my ($wd) = $0 =~ m-(.*)/- ;
   $wd ||= '.';
-  # FIXME: currently the bs_srcserver makes assumptions on being in a
-  # properly set up working dir, e.g. with subdirs 'worker' and
-  # 'build'.  Either that is cleaned up or this stays in, for the sake
-  # of startproc and others being able to start a bs_srcserver without
-  # knowing that it has to be started in the right directory....
-
-  chdir "$wd";
   unshift @INC,  "build";
   unshift @INC,  ".";
 }
 
-use Types::Serialiser;
 use JSON::XS ();
 use MIME::Base64 ();
 use Digest::SHA ();