These must be executed directly in an include file. Whether it is in functions.php or in another include file, these cannot be wrapped in a hook. They won't work on init or any other I have found so far.
They can also be included directly in a template like page.php to execute only for that template.
NOTE: DO NOT INCLUDE THIS IN A DISTRIBUTED THEME OR PLUGIN (unless it is disabled by default, like not including the include file it's in unless the user specifies).
This is bad practice to include in a site you don't control because it can and will break the output of any other themes or plugins.
// Remove the auto-paragraph and auto-line-break from the content
remove_filter( 'the_content', 'wpautop' );
// Remove the auto-paragraph and auto-line-break from the excerpt
remove_filter( 'the_excerpt', 'wpautop' );
/**
* Remove the automatic line breaks from content and excerpts.
*
* @since 1.0.0
*/
function remove_content_auto_line_breaks() {
// Remove the auto-paragraph and auto-line-break from the content
remove_filter( 'the_content', 'wpautop' );
// Remove the auto-paragraph and auto-line-break from the excerpt
remove_filter( 'the_excerpt', 'wpautop' );
}
// Execute the function
remove_content_auto_line_breaks();