ci: Drop nightly job that builds CMake with vendored curl on macOS

Revert commit 31884a7146 (ci: Add nightly job to build CMake with
vendored curl on macOS, 2024-05-09, v3.30.0-rc1~130^2).  After
curl 8.15.0 dropped support for the Secure Transport backend, we
rely on the curl provided by macOS to use the system certificate
store.