tools: remove mockery from tools.go (#9196)

The `mockery` project recommends against using a binary of `mockery` that has been created using `go install`. https://github.com/vektra/mockery/pull/456. Developers of Tendermint wishing to generate mocks should avoid having a version of `mockery` on their path that does not match the version listed in  [mockery_generate.sh](10e1ac8fea/scripts/mockery_generate.sh (L11)). To make this easier for developers, the `mockery_generate.sh` script uses a containerized copy of `mockery` if `mockery` is not present on the developer's `PATH`. This containerized version of `mockery` uses the same version of mockery as our CI pipelines and allows all developers to automatically use the same version without having to manage it themselves. 

#### PR checklist

- [ ] Tests written/updated, or no tests needed
- [ ] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [ ] Updated relevant documentation (`docs/`) and code comments, or no
      documentation updates needed

.github/workflows/check-generated.yml

@@ -26,8 +26,6 @@ jobs:
         run: |
           set -euo pipefail
 
-          readonly MOCKERY=2.12.3  # N.B. no leading "v"
-          curl -sL "https://github.com/vektra/mockery/releases/download/v${MOCKERY}/mockery_${MOCKERY}_Linux_x86_64.tar.gz" | tar -C /usr/local/bin -xzf -
           make mockery 2>/dev/null
 
           if ! git diff --stat --exit-code ; then