refactor: Removes the deprecated CLIENT_CACHE feature flag

[michael-s-molina]

SUMMARY

As part of the 4.0 approved initiatives, this PR removes the CLIENT_CACHE feature flag.

The previous value of the feature flag was False and now the feature is permanently removed.

TESTING INSTRUCTIONS

CI should be sufficient for merging this PR. We'll do a complete testing of 4.0 after all approved proposals are merged.

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (2d3ff8c) 69.07% compared to head (1994bea) 69.07%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #26348   +/-   ##
=======================================
  Coverage   69.07%   69.07%           
=======================================
  Files        1931     1931           
  Lines       75329    75323    -6     
  Branches     8431     8429    -2     
=======================================
- Hits        52030    52028    -2     
+ Misses      21151    21148    -3     
+ Partials     2148     2147    -1     

Flag	Coverage Δ
hive	53.60% <ø> (ø)
javascript	56.47% <100.00%> (+<0.01%)	⬆️
mysql	77.91% <ø> (ø)
postgres	78.01% <ø> (ø)
presto	53.55% <ø> (ø)
python	82.76% <ø> (ø)
sqlite	77.59% <ø> (ø)
unit	55.83% <ø> (ø)

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[john-bodley]

@betodealmeida I thought you might be the ideal person to review this given you added the feature in #7348 likely to handle a specific use case for Lyft.

[justinpark]

LGTM