math/py-igraph: Update to 0.10.6

• Switch to DISTVERSION
• Always use Flex from ports
• Use available dependencies in tree instead of vendored This is also consistent with math/igraph

Changelog:
https://github.com/igraph/python-igraph/releases/tag/0.10.6

PR: 273168
Reviewed by: lwhsu (maintainer)
Sponsored by: Blinkinblox