chore: remove orphaned semver.sh helper (MetaMask#9172)

## Explanation

`scripts/semver.sh` was only sourced by `scripts/migrate-tags.sh`, which
is being removed in MetaMask#9171. With that script gone, `semver.sh` is
orphaned, so this PR deletes it too.

## References

- Follow-up to MetaMask#9171

## Checklist

- [ ] I've updated the test suite for new or updated code as appropriate
- [ ] I've updated documentation (JSDoc, Markdown, etc.) for new or
updated code as appropriate
- [ ] I've communicated my changes to consumers by [updating changelogs
for packages I've
changed](https://github.com/MetaMask/core/tree/main/docs/processes/updating-changelogs.md)
- [ ] I've introduced [breaking
changes](https://github.com/MetaMask/core/tree/main/docs/processes/breaking-changes.md)
in this PR and have prepared draft pull requests for clients and
consumer packages to resolve them

Author: cryptodev-2s