Merge #21437: gitian, ci: Drop unneeded python3-dev package for macOS builds

e4c0cada79 ci, gitian: Drop unneeded python3-dev package for macOS builds (Hennadii Stepanov)

Pull request description:

ACKs for top commit:
  fanquake:
    ACK e4c0cada79 - gitian builds match and I checked that this doesn't end up installed as a side-effect of another package.

Tree-SHA512: 520a3909b106a0e005b195c5395691edf62b76ee2df43b6971b7aa193648d68e6dac69cb4f1dc474f594b015a2fc2074061865e571d89365174beb5c1780356f

contrib/gitian-descriptors/gitian-osx.yml

@@ -23,7 +23,6 @@ packages:
 - "imagemagick"
 - "libz-dev"
 - "python3"
-- "python3-dev"
 - "python3-setuptools"
 - "fonts-tuffy"
 - "xorriso"