Clean up release scripts.

Clean up release scripts.

This makes some internal renaming, e.g. trunk -> candidates,
bleeding edge -> master, without changing the api.

Also remove some unused bailout steps from the push script.

Remove unused bump version script.

BUG=chromium:451975
TBR=tandrii@chromium.org
NOTRY=true
LOG=n

Review URL: https://codereview.chromium.org/873213002

Cr-Commit-Position: refs/heads/master@{#26269}