Ported Layer::merge_slices() to XS

lib/Slic3r/Layer.pm

@@ -32,11 +32,6 @@ sub regions {
     return [ map $self->get_region($_), 0..($self->region_count-1) ];
 }
 
-sub merge_slices {
-    my ($self) = @_;
-    $_->merge_slices for @{$self->regions};
-}
-
 sub make_perimeters {
     my $self = shift;
     Slic3r::debugf "Making perimeters for layer %d\n", $self->id;