Always allow cross origin requests

[iFergal]

Feature request description/rationale

KERI_AGENT_CORS allows CORS for any Signify clients running in browser or WebView environments. So far there's no real need to be strict on CORS, at least until we get an admin dashboard or something.

So we can remove the env var, and always have loose CORS rules.

[kentbull]

agreed, let's just have them always be enabled.