removed the Event model, table, and related services and api payloads

this was not used and will instead be replaced by a Request specific API endpoint
Config should raise an error if both file and env configs are available

We use file configs for some apps and ENV config for the others. When
both configs are available (for example because someone accidentally set
an ENV config where file config is already set), Travis.config will
silently prefer ENV over file config.

This commit raises an error in such situation