• Add a new setting enable_custom_logo = 1 under [General] in the config
• When feature is disabled, throw an exception in CoreAdminHome.setBrandingSettings API
• When feature is disabled, do not show the div for that setting in CoreAdminHome/generalSettings.twig.
• When feature is disabled, throw an exception in CoreAdminHome controller in uploadCustomLogo action.

We don't need to change anything else.