Because the release_bot mixin includes the 'static' config,
the shared-library bots included both 'static' and 'shared'.

This removes the wrong 'static' config.

BUG=chromium:474921
TBR=vogelheim@chromium.org, jochen@chromium.org

Review-Url: https://codereview.chromium.org/2123243002
Cr-Commit-Position: refs/heads/master@{#37556}