[3.6] Make codecov config on master the only config used (GH-2041) (GH-2052)

This will allow for centralized management of the Codecov config to prevent skew as well as easier management going forward.

Closes python/core-workflowGH-81.
(cherry picked from commit 11ffb4543bc000dea527bcc0417e2f8bda13790f)
1 file changed