Probably it could use prune_libtool_files (from eutils.eclass) to drop them (but I am unsure if maybe they are preserved for some reason...) Thanks
[master 37996d4a4b1] dev-scheme/guile: Don't install .la files, neither build static always (#592088) 1 file changed, 83 insertions(+) create mode 100644 dev-scheme/guile/guile-2.0.14-r1.ebuild