===================
server {
    listen 80;
    server_name example1.com example2.com;
===================

I tried to setup the WWW to non-WWW redirect like this in an additional server directive:

===================
server {
    server_name www.example1.com;
    return 301 $scheme://example1.com$request_uri;
}
===================

I also tried the older method:

===================
server {
    server_name www.example1.com;
    rewrite ^/(.*)$ http://example1.com/$1 permanent;
}
===================