Single Staking menu

[vbaranov]

Motivation

3 menu items related to Staking Dapp:

The idea is to replace with a single menu item

Changelog

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[coveralls]

Pull Request Test Coverage Report for Build 904cc67eecff61d9057358140da7ec5da732459b-PR-3557

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.1%) to 66.827%

---

Totals
Change from base Build 0fa15045632b59c7d31418502651b6f366e6a03b:	1.1%
Covered Lines:	2079
Relevant Lines:	3111

---

💛 - Coveralls