Since these commits:
* commit ab2276e6b9 (Utilities/Release: remove old macOS release script,
2020-09-16)
* commit 7670ba8b0a (Utilities/Release: Drop win{32,64} scripts in favor
of docker build, 2020-05-05, v3.18.0-rc1~203^2)
* commit 689fdbfc61 (Utilities/Release: Drop linux64 script in favor of
docker build, 2019-08-27, v3.16.0-rc1~184^2)
several scripts we once used for producing release binaries for
distribution on `cmake.org` are no longer needed.
These will allow anyone to produce portable binaries like those
published on `cmake.org`.
Follow the pattern from commit facc240a45 (Utilities/Release: Add docker
specs to build and test Linux binaries, 2019-08-23, v3.16.0-rc1~184^2~2).
Parameterize the architecture to support both `x86_64` and `i386`.
The spec added by commit facc240a45 (Utilities/Release: Add docker specs
to build and test Linux binaries, 2019-08-23) generates only the TGZ
package, but the old `Utilities/Release/linux64_release.cmake` script
also generated a STGZ package.
