Skip post package for static library when building header only

[uilianries]

• Post package for header-only is already validated. No artifacts is expected
• When is a header-only package, ignores shared=False on post package.

fixes #456

/cc @toge

[SpaceIm]

Should this logic also be added to _shared_files_well_managed()?

[SpaceIm]

I think this PR should be reverted. Hook behaved properly in https://github.com/conan-io/conan-center-index/pull/14330 (https://github.com/conan-io/hooks/issues/456), miniaudio recipe was not removing shared option in configure() when header_only option was True.