tree: `--graph-features` -> `--edges default` transition not followed in shell completions

[chrysn]

The original PR for cargo tree (#8062) indicated a new --graph-features flag. That was practically renamed to --edges features in the course of the PR's evolution, but stuck in the shell completions.

Currently, src/etc/cargo.bashcomp.sh and src/etc/_cargo both still refer to --graph-features and do not include the --edges option.