PM-34085: Chore: Remove the Authenticator Sync backwards compatibility

[david-livefront]

🎟️ Tracking

PM-34085

📔 Objective

This PR removes the backwards compatibility of the Authenticator Sync in order to clear up the implementation. This changes means that in order for the sync functionality to work properly both the Password Manager and Authenticator must be running v2026.4.0 or later.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 85.90%. Comparing base (83a9d35) to head (f4e498f).

Files with missing lines	Patch %	Lines
...tor/repository/util/SharedAccountDataExtensions.kt	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6928      +/-   ##
==========================================
- Coverage   86.37%   85.90%   -0.47%     
==========================================
  Files         864     1010     +146     
  Lines       62618    65256    +2638     
  Branches     9104     9179      +75     
==========================================
+ Hits        54085    56060    +1975     
- Misses       5404     6047     +643     
- Partials     3129     3149      +20     

Flag	Coverage Δ
app-data	17.17% <0.00%> (+<0.01%)	⬆️
app-ui-auth-tools	19.65% <0.00%> (+0.30%)	⬆️
app-ui-platform	16.15% <0.00%> (+0.62%)	⬆️
app-ui-vault	28.79% <0.00%> (+0.56%)	⬆️
authenticator	6.30% <0.00%> (-0.03%)	⬇️
lib-core-network-bridge	4.11% <50.00%> (+0.01%)	⬆️
lib-data-ui	1.13% <0.00%> (+<0.01%)	⬆️

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