Add support for Erlang (*.erl) files.
Drop `apache-` prefix for default-license tests.

If the license is unspecified, the Apache 2.0 license is automatically selected.
This change renames the files that use this behavior to remove the `apache-`
prefix because the because the naming convention is
`[optional license]-[optional company]-[language].*` and the Apache license is
not specified in these tests.