We introduced releases_page feature flag.
Given this feature is deemed stable, we should remove
this flag before 19th.

Updates specs to use new rails5 format.

The old format:
`get :show, { some: params }, { some: headers }`

The new format:
`get :show, params: { some: params }, headers: { some: headers }`

Rename Projects::ReleasesController to
Projects::Tags::ReleasesController

This whitelists all existing places where we use "destroy_all".