par2script: don't bother removing already removed parts of arguments

the s/\@// conflicts with jenkins default directory naming for
concurrent builds and is wrong at this place/in this form:
0ce067c1 already changed the format of
the parameter from @listfile to @@listfile, so stripping a single @ at
the front won't help at all.
Furthermore the stripping already was added to the
par2script/parameters.pm earlier, so the worker functions don't need to
deal with transforming commandline arguments.

Change-Id: Ic55b8cda3cd114dfc5cb7ded6d53174cd8283af9
Reviewed-on: https://gerrit.libreoffice.org/55196Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

solenv/bin/modules/par2script/work.pm

@@ -79,8 +79,6 @@ sub setparfiles
     my ($filename) = @_;
 
     # input is the name of the list file
-    $filename =~ s/\@//;    # removing the leading \@
-
     my $filecontent = par2script::files::read_file($filename);
 
     my @parfiles = ();