Remove artificial dependency on XML::Simple

The only part of the xref-mapping pipeline that depended on the
long-deprecated module XML::Simple was TAIROntologyParser - which did
not actually *use* that module for anything. Get rid of the useless
import, thus making it unnecessary for XML::Simple to be mentioned in
the cpanfile.

cpanfile

@@ -31,6 +31,5 @@ feature 'xref_mapping', 'Xref mapping pipeline' => sub {
   requires 'Digest::MD5';
   requires 'Text::Glob';
   requires 'XML::LibXML';
-  requires 'XML::Simple';
 };
 =cut

misc-scripts/xref_mapping/XrefParser/TAIROntologyParser.pm

@@ -102,7 +102,6 @@ use Data::Dumper;
 use File::Basename 'basename';
 use Readonly;
 use List::MoreUtils 'uniq';
-use XML::Simple 'XMLin';
 
 use base qw( XrefParser::BaseParser );