Much easier way I found (in newer builds overriding didn't help).
First install Package Resource Viewer.
Extract "PHP" package (ctrl+shift+p -> extract -> select PHP). If PHP is not there, most probably you already have it extracted in your Packages folder, so delete it.
Enter the extracted PHP directory and run
or remove all snippets, BUT NOT the other files.
Rename this directory to something like PHPCustom (this step leaves syntax and other PHP stuff, but not the snippets).
Add PHP to ignored packages in the settings