Differentiate 'EE-without-a-license' from 'EE-with-an-old-license' in usage pings

Now that we have people install EE by default, but let it operate in CE mode if you don't have a license, we need to be able to report that via usage pings. It seems we're reporting that currently as EE, but old licenses, before the introduction of EES and EEP also report as EE, so we can't tell them apart. It's possible for us to recreate the information based on license_starts_at, but it would helpful to have this in the usage ping itself.

/cc @smcgivern