Adds back GSS build flag and disables the feature

[antonis]

Depends on wordpress-mobile/WordPress-FluxC-Android#2068

Description

This PR reverts the changes applied with #15050 and disables Global Style Settings feature by default.
This is a temporary change to unblock 1.58 gutenberg-mobile release.

To test:

Verify that this reported issue does not occur with the APK from this PR.
⚠️ Note: Please uninstall the any previous version of the app that exhibited the bug to avoid getting cached data

Regression Notes

1. Potential unintended areas of impact
   N/A

2. What I did to test those areas of impact (or what existing automated tests I relied on)
   N/A

3. What automated tests I added (or what prevented me from doing so)
   N/A

PR submission checklist:

• I have completed the Regression Notes.
• I have considered adding accessibility improvements for my changes.
• I have considered if this change warrants user-facing release notes and have added them to RELEASE-NOTES.txt if necessary.

[peril-wordpress-mobile]

You can trigger optional UI/connected tests for these changes by visiting CircleCI here.

[SiobhyB]

I confirmed I'm no longer seeing the error while checked out locally:

Screen.Recording.2021-07-22.at.17.53.12.mov

I'm able to return to edit a post without issue. 🎉

[fluiddot]

LGTM 🎊 !

I verified that the freezing upon opening is not happening, as well as that colors match the site's theme.