Completely remove the JSON dependency by switching PG to using Mojo::JSON as well.

Author: drgrice1

bin/check_modules.pl

@@ -107,7 +107,6 @@ =head1 DESCRIPTION
 	IO::Socket::SSL
 	Iterator
 	Iterator::Util
-	JSON
 	Locale::Maketext::Lexicon
 	Locale::Maketext::Simple
 	LWP::Protocol::https

conf/defaults.config

@@ -1363,7 +1363,7 @@ ${pg}{modules} = [
 	[qw(PGcore PGalias PGresource PGloadfiles PGanswergroup PGresponsegroup Tie::IxHash)],
 	[qw(Locale::Maketext)],
 	[qw(WeBWorK::PG::Localize)],
-	[qw(JSON)],
+	[qw(Mojo::JSON)],
 	[qw(Rserve Class::Tiny IO::Handle)],
 	[qw(DragNDrop)],
 	[qw(Types::Serialiser)],