Fix: mysql information displays properly in WP 6.4

[JasonTheAdams]

Description

WordPress has held backwards compatibility for the MySQL PHP extension for a long time, and provided the $wpdb->use_mysqli property as a way of checking if a WP instance is using the old extension, or the new(er) mysqli extension.

In WP 6.4, support for the old extension is being dropped, due to the fact that the extension doesn't exist in PHP 7.0, which is the new minimum required version of WordPress. With this, WP is also dropping the $wpdb->use_mysqli property because it's meaningless.

Our code was using both that property and, conditionally, the function the used the old extension. Since we don't support <PHP 7.2, we can also drop the use of that function and WP property.

Affects

The MySQL portion of the system info page

Testing Instructions

Make sure that the MySQL info loads properly on WP 6.3 and 6.4.

Pre-review Checklist

• Self Review of code and UX completed

[pauloiankoski]

Lovely deletion PR.

[rickalday]

Passed manual QA tests.