Don't use existing configuration on Override classes [#2969131]

Problem

Quite a few configuration overrides in Open Social load the current configuration and include that configuration in the overrides array. This causes the entire configuration object to be marked as overwritten which can lead to problems if someone else wants to do the same.

It's also unnecessary because configuration overrides are performed using a deep merge which means that only the final leaf of the overrides object is used for the override.

Solution

Remove loading of configuration that's put into the returned $overrides array for all Override classes.

A quick search sees this pattern in the following classes but a more thorough search may be required.

modules/custom

SocialFilePrivateFieldsConfigOverride
SocialFilePrivateTExtEditorConfigOverride
SocialLanguageConfigOverride

modules/features

SocialEmbedConfigOverride
SocialProfileFieldsOverride
SocialMentionsConfigOverride
SocialTaggingOverrides
SocialGroupSelectorWidgetConfigOverride
SocialEventTypeConfigOverride
SocialEmbedEditorConfigOverride
SocialLikeConfigOverride
SocialPostPhotoConfigOverride
SocialEventManagersConfigOverride
SocialLandingPageConfigOverride
SocialBookConfigOverride

An example commit where we already made these changes: https://github.com/goalgorilla/open_social/pull/789/commits/cbf58984f94e...

An example (merged) pull request that made these changes:
https://github.com/goalgorilla/open_social/pull/850

Tasks

Create an issue for each class/module to keep individual changes small and easily reviewable. This also makes it possible for discussion around 1 class that may be special to not block all the others. Make those issues a child issue of this issue and update the list above to link to it.
Perform a more extensive search than a quick grep for config.*get in *Override* files
Fix all the issues