[edn/doc] Clarify number of end points in block diagrams

`edn_blk_diag.svg` previously had `NumEndPoints=4`, but EDN currently
only supports `NumEndPoints=8`.

`edn_top_diag.svg` has one EDN instance with four end points connected
and one instance with three end points connected.  This is supported by
EDN, but `NumEndPoints` must remain at 8 and the unused end points must
be tied off.  Additionally, that diagram named the end points (e.g.,
`aes`, `kmac`, `otbn`), which may suggest that this diagram represents
the topology of any actual implementation, which is not the case.  To
avoid this, those names have been replaced by 'anonymous' designators
(`ep0` and so on).

This commit updates the two diagrams to reflect what EDN currently
supports.

The two diagrams were originally drawn in Visio and exported to SVG.  As
there's no open-source tool available to edit Visio files in general
(and I don't have one installed specifically), those files become
outdated.  To prevent stale/divergent information from being kept in the
repository, this commit removes the Visio files.

Signed-off-by: Andreas Kurth <[email protected]>