Remove duplicate console command for --keep flag

[derekblank]

When testing patch releases, I noted that there are duplicate console.Info declarations in the CLI when running the prepare command with the --keep flag:

[INFO] Finished preparing Gutenberg Mobile PR
[INFO] 
Finished preparing PRs:
https://github.com/derekblank/gutenberg/pull/30
https://github.com/derekblank/gutenberg-mobile/pull/9
[INFO] Keeping temporary directory /var/folders/xk/xmtl5xjx33v_bp94749wm0j00000gn/T/gbm-1558918830
[INFO] Keeping temporary directory /var/folders/xk/xmtl5xjx33v_bp94749wm0j00000gn/T/gbm-1558918830

This PR removes the console.Info in setCleaner.

Testing

1. Run prepare all with the --keep flag, e.g.: go run main.go release prepare all 1.115.2 --keep
2. Note only one "Keeping temporary directory [...]" line is logged to the console.

[jhnstn]

Nice!