drop pseudonym scope, legacy format/hash support

[eschultink]

A couple things to note:

• legacy pseudonyms hashed with scope; but had scope == null in the email case; so legacy hashes of emails and v0.4 hashes of emails are byte-wise equivalent, although there is a minor encoding difference. legacy pseudonyms invented a url-safe encoding (replacing + and / with _ and .), instead of using the standard RFC one (_ and-).

Features

• remove deprecated notions of pseudonym scope, legacy format support, transitional fiels (h_4)

Change implications

• dependencies added/changed? no
• something important to note in future release notes? yes; no one using legacy pseudonyms should upgrade; must be migrated to the new ones first