What does a piece of code mean?

Question

1C-Bitrix

on the hosting in the public_html folder there are folders and files of the site, there is also a folder with files responsible for the subdomain. a site on the main domain on Bitrix, on a subdomain it is not clear on what. at the root of the site there is a .htaccess file, where there is a piece

<IfModule mod_rewrite.c>
  Options +FollowSymLinks
  RewriteEngine On

  RewriteCond %{HTTP_HOST} ^www\.example\.ru$ [NC]
  RewriteRule ^(.*)$ http://example.ru/$1 [R=301,L]

  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-l
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteCond %{REQUEST_FILENAME} !/bitrix/urlrewrite.php$
  RewriteRule ^(.*)$ /bitrix/urlrewrite.php [L]
  RewriteRule .* - [E=REMOTE_USER:%{HTTP:Authorization}]
</IfModule>

The whole problem is that the subdomain only works if you remove this piece. If you leave it, not a single style and script file is connected at all. What's going on in this part, can anyone explain? And is it possible to unrestrictedly delete this place or do I need to fix something to make it work?