[use-cases] issuing updates

[gkellogg]

• Remove redundant and un-informative credential creation workflow diagrams.
• Add most remaining issuer use cases.

[gkellogg]

The remaining raw content for issuing not noted as used probably require more discussion or may be redundant.

[gkellogg]

Also note that this is a fairly raw move; we should triage before spending too much time in word-smithing and coordinating stylistic changes, IMO.