Site Health: Simplify the checks for constants in debug information

[xkon]

Following the changes in #46692 there are constants that are defined by default. There's no need to check again if they are not defined so we can simplify things a bit in debug info for wp-constants.

We should also change the informational title of this section from These settings are defined in your wp-config.php file, and alter where and how parts of WordPress are loaded. as not all of them are actually defined in wp-config.php.

[xkon]

46738.diff​ changes the title into "These settings alter where and how parts of WordPress are loaded." and simplifies the checks/output of constants.

[SergeyBiryukov]

Looks good to me.

[SergeyBiryukov]

In 45078:

Site Health: Simplify the checks for constants that are always defined by default.

Props xkon.
Fixes #46738.