Is checking whether the blog is installed necessary?

My WordPress site has become kinda slow and unresponsive, so I am trying what can I do to speed it up by eliminating unnecessary database queries and other things.
I stumbled across suggestion found at https://yoast.com/wordpress-performance-optimization where it says that the function is_blog_installed is useless on running site. https://codex.wordpress.org/Function_Reference/is_blog_installed The comments on article are from 2009. Can we safely remove it without breaking anything now or in the future?

 1. open up wp-includes/functions.php 
 2. find the function is_blog_installed() 
 3. add return true; as the first line of the function

You Could, but I would never ever mess with core files.

Apart from that I do not believe that the is_blog_installed() function causes your site to be unresponsive.
Try disabling all plugins first, and set the theme to one of the default themes.
Updating your site, plugins and themes could help you as well. Try to narrow your problem down. I suspect it’s either in a theme or plugin.