Bootstrap/Load: Remove the `wp_environment_type` and `wp_get_environment_type` filters.

Since `wp_get_environment_type()` runs too early for plugins to hook these filters, and the result is then cached in a static variable and cannot be changed later, the filters are not that useful.

The `WP_ENVIRONMENT_TYPES` and `WP_ENVIRONMENT_TYPE` constants and environment variables should be enough for now.

Follow-up to [47919], [48188], [48372].

Props Clorith, SergeyBiryukov.
Fixes #33161.
Built from https://develop.svn.wordpress.org/trunk@48662


git-svn-id: https://core.svn.wordpress.org/trunk@48424 1a063a9b-81f0-0310-95a4-ce76da25c4cd