Don't cache inline repos

[Guldoman]

When specifying inline repos like in lpm run --ephemeral http://url.to/repo:branch plugin_name, the repo gets cached, but can't be updated with lpm update, so even if the inline repo changes, it's never updated.

So lpm could either avoid caching those, or try to always update them before using them.
Avoiding caching them would save space that at the moment never gets reclaimed.