Remove Redis cluster support

[zhenghaoz]

Remove Redis cluster support since RediSearch is inavailable on Redis cluster.

[codecov]

Codecov Report

Patch coverage: 60.00% and project coverage change: +0.11 🎉

Comparison is base (0999f74) 70.43% compared to head (3b15770) 70.54%.

❗ Current head 3b15770 differs from pull request most recent head 3d46a16. Consider uploading reports for the commit 3d46a16 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #645      +/-   ##
==========================================
+ Coverage   70.43%   70.54%   +0.11%     
==========================================
  Files          63       63              
  Lines       12518    12392     -126     
==========================================
- Hits         8817     8742      -75     
+ Misses       2851     2815      -36     
+ Partials      850      835      -15     

Impacted Files	Coverage Δ
storage/cache/database.go	76.19% <ø> (+5.30%)	⬆️
storage/cache/redis.go	85.81% <60.00%> (+10.14%)	⬆️

... and 1 file with indirect coverage changes

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