* package api: drop wildcard re-export
To ensure package repos are forward/backward compatibility with Spack,
we should explicitly export all symbols we want to expose in the public
package API, and drop `from spack.something import *` because
removal/addition to the public API will go unnoticed.
Also `llnl.util.filesystem` has some methods that shouldn't be exposed
in the package API, so better to enumerate a subset explicitly.
* remove flatten_dependencies / install_dependency_symlinks
92260b179d