Merge #21354: build, doc: Drop no longer required packages from macOS cross-compiling dependencies

f7f3829a68 build, doc: Drop libbz2-dev from macOS cross-compiling dependencies (Hennadii Stepanov)
d8239362e2 build, doc: Drop libcap-dev from macOS cross-compiling dependencies (Hennadii Stepanov)

Pull request description:

  The `libcap-dev` and `libbz2-dev` packages are no longer required when cross-compiling for macOS.

ACKs for top commit:
  fanquake:
    ACK f7f3829a68

Tree-SHA512: 820cdc2724f3346c0942d4d4115fc7206f7bf02889d9fa6cbdbd1d9e3afa03a067c1c3fa64dff596aefdc74898178b7c7d64027a6501486e3b606f4760de04ae

contrib/gitian-descriptors/gitian-osx.yml

@@ -21,9 +21,7 @@ packages:
 - "bsdmainutils"
 - "cmake"
 - "imagemagick"
-- "libcap-dev"
 - "libz-dev"
-- "libbz2-dev"
 - "python3"
 - "python3-dev"
 - "python3-setuptools"