In some cases, a user might pull a ref into the local repository and
not deploy it by using FLATPAK_INSTALL_FLAGS_NO_DEPLOY. Later on, that
user might decide that they don't want to deploy the ref after all,
but there was no way to remove that ref from the local repository
in the public API, so it takes up disk space.
Add flatpak_installation_remove_local_ref_sync to remove a given
ref from the local repository if the ref is known and
flatpak_installation_cleanup_local_refs_sync to remove all undeployed
refs.
Fixes#1031Closes: #1034
Approved by: alexlarsson