Remove completed items from TODO list

Download progress bars were implemented in
ff42fcb and refined in later commits.

Dependency graph visualization is now handled by codezoom, a separate
project now in the apposed org: https://github.com/apposed/codezoom.
Codezoom uses jgo to resolve dependency graphs for Java projects. :-)
Therefore, we remove the old bin/viz.sh graphviz script.

Author: ctrueden

TODO.md

@@ -91,8 +91,6 @@ These can be deferred to 2.1.0 or later:
 Ideas for future releases (not tracked in this file, move to GitHub issues):
 
 - (HIGH) Parallel downloads for faster cache population
-- (HIGH) Progress bars for downloads
-- (HIGH) Dependency graph visualization (add --graphviz or similar output mode to tree/list/info)
 - (HIGH) Shell completion (bash/zsh)
 - (MEDIUM) Version ranges with semantic versioning
   - E.g. report on dependency divergence in desired scenarios (e.g. two different major versions)