import: utils: 'recursive-import' returns a list rather than a stream.

import: utils: 'recursive-import' returns a list rather than a stream.

* guix/import/utils.scm (recursive-import): Remove 'list->stream' call.
* guix/scripts/import/cran.scm (guix-import-cran): Remove 'stream->list'
call.
* guix/scripts/import/crate.scm (guix-import-crate): Likewise.
* guix/scripts/import/elpa.scm (guix-import-elpa): Likewise.
* guix/scripts/import/gem.scm (guix-import-gem): Likewise.
* guix/scripts/import/hackage.scm (guix-import-hackage): Likewise.
* guix/scripts/import/opam.scm (guix-import-opam): Likewise.
* guix/scripts/import/pypi.scm (guix-import-pypi): Likewise.
* guix/scripts/import/stackage.scm (guix-import-stackage): Likewise.
* tests/gem.scm ("gem-recursive-import"): Likewise.
* tests/import-utils.scm ("recursive-import"): Likewise.

Co-authored-by: Brian Leung <bkleung89@gmail.com>