Remove ci_create_partitions_102 feature flag

What does this MR do and why?

Cleanup after !148376 (merged)

The partitions are created on the CI database:

marius@rocket-sled ~/W/g/gitlab (master)> pgai connect ci
Preparing clone ... [====================]
ℹ info    Data state at: 2024-05-08 04:45:40 UTC
Timing is on.
psql (14.11 (Homebrew), server 14.10 (Debian 14.10-1.pgdg110+1))
Type "help" for help.

gitlabhq_dblab=# select parent_identifier, identifier from postgres_partitions where condition ilike '%102%' order by parent_identifier;
         parent_identifier         |                       identifier
-----------------------------------+--------------------------------------------------------
 public.p_ci_build_names           | gitlab_partitions_dynamic.ci_build_names_102
 public.p_ci_builds                | gitlab_partitions_dynamic.ci_builds_102
 public.p_ci_builds_metadata       | gitlab_partitions_dynamic.ci_builds_metadata_102
 public.p_ci_job_annotations       | gitlab_partitions_dynamic.ci_job_annotations_102
 public.p_ci_job_artifacts         | gitlab_partitions_dynamic.ci_job_artifacts_102
 public.p_ci_pipeline_variables    | gitlab_partitions_dynamic.ci_pipeline_variables_102
 public.p_ci_runner_machine_builds | gitlab_partitions_dynamic.ci_runner_machine_builds_102
 public.p_ci_stages                | gitlab_partitions_dynamic.ci_stages_102
(8 rows)

And the main database:

marius@rocket-sled ~/W/g/gitlab (454519-mb-remove-102-ff)> pgai connect main
Preparing clone ... [=================================================]
ℹ info    Data state at: 2024-05-08 02:14:53 UTC
Timing is on.
psql (14.11 (Homebrew), server 14.10 (Debian 14.10-1.pgdg110+1))
Type "help" for help.

gitlabhq_dblab=# select parent_identifier, identifier from postgres_partitions where condition ilike '%102%' order by parent_identifier;
         parent_identifier         |                       identifier
-----------------------------------+--------------------------------------------------------
 public.p_ci_build_names           | gitlab_partitions_dynamic.ci_build_names_102
 public.p_ci_builds                | gitlab_partitions_dynamic.ci_builds_102
 public.p_ci_builds_metadata       | gitlab_partitions_dynamic.ci_builds_metadata_102
 public.p_ci_job_annotations       | gitlab_partitions_dynamic.ci_job_annotations_102
 public.p_ci_job_artifacts         | gitlab_partitions_dynamic.ci_job_artifacts_102
 public.p_ci_pipeline_variables    | gitlab_partitions_dynamic.ci_pipeline_variables_102
 public.p_ci_runner_machine_builds | gitlab_partitions_dynamic.ci_runner_machine_builds_102
 public.p_ci_stages                | gitlab_partitions_dynamic.ci_stages_102
(8 rows)

Time: 263.559 ms

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Related to #454519 (closed)