Remove five unused @babel/* devDependencies

The five @babel/* packages were added for a babel-jest transform when
Octokit became ESM-only and Jest was still CommonJS. Switching to Vitest
removed the Jest packages but left these behind, and nothing has used
them since: the build is esbuild, tests are Vitest, and there is no
Babel config or import anywhere in the repo.

Removing them resolves the Dependabot deadlock in #1450, #1439, #1431
and #1430, where each PR moves only half of a mutually-dependent set and
so fails npm ci with ERESOLVE.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 65a4db01-44b3-42c3-9459-ab3d251ebac9

Author: henrymercer