Remove the duplicated `other_storage_counter` app

What does this MR do?

It removes the other_storage_counter app introduced in !57121 (merged) with all related changes. It's being removed because the main epic https://gitlab.com/groups/gitlab-org/-/epics/5488#note_654574160 has been marked as won't do and the introduced code won't be used anymore.

Note: the pipelines (danger) are failing because the MR removes a feature flag without adding a changelog, the reason we didn't add a changelog is that we're removing the feature flag and the code associated with it.

Screenshots

before	after

How to setup and validate locally (strongly suggested)

To validate before checking out the branch:

1. enable `Feature.enabled(:other_storage_tab)
2. visit a groups usage quotas groups/<ID>/-/usage_quotas
3. observe the last tab "Other Storage"

To validate after checking out the branch:

1. visit a groups usage quotas groups/<ID>/-/usage_quotas
2. observe the last tab "Other Storage" is not there
3. (optional) disable the feature flag Feature.disable(:other_storage_tab)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
  • It's not needed, given the code is behind a feature flag and didn't have a changelog to be reverted.
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Related to #334892