Remove unused statistics collection

[onurctirtir]

DESCRIPTION: Stops on-demand statistics collection for clusters and deprecates citus.enable_statistics_collection GUC.

[codecov[bot]]

Codecov Report

:x: Patch coverage is 66.66667% with 3 lines in your changes missing coverage. Please review. :white_check_mark: Project coverage is 89.12%. Comparing base (95477e6) to head (c7a55c8). :warning: Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8174      +/-   ##
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+ Coverage   88.95%   89.12%   +0.17%     
==========================================
  Files         287      286       -1     
  Lines       63136    63006     -130     
  Branches     7941     7928      -13     
==========================================
- Hits        56163    56156       -7     
+ Misses       4663     4539     -124     
- Partials     2310     2311       +1     

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[onurctirtir]

Should remove citus_server_id() in 14.0 sql script once https://github.com/citusdata/citus/pull/8170/ is merged.

update: No, won't remove it as it's still indirectly used by IsWorkerTheCurrentNode(). In other words, we should still have server_id in pg_dist_node_metadata, which is generated by citus_server_id().