[FEATURE]: Remove the “Custom Fields” meta box

[jakewrfoster]

Description

Alleyvate should remove the "Custom Fields" meta box. This is currently happening in our wp-starter-theme and should be removed there when added to Alleyvate.

Use Case

Core's "Custom Fields" meta is never used in the course of our WordPress development. As such it is unnecessary visual clutter that when removed presents a cleaner user experience.

[jakewrfoster]

Issue originally raised by @kaitlinbolling