Remove skip_epic_count_visibility_check feature flag
What
Remove the :skip_epic_count_visibility_check
feature flag.
Related to !35129 (comment 368049157)
Owners
- Team: Plan team
- Most appropriate slack channel to reach out to: `#g_plan
- Best individual to reach out to: jprovaznik
Expectations
### What are we expecting to happen?
The feature is enabled by default, with the feature enabled group show page should load faster.