max_conns and max_idle_conns are not removed from DSN

[vesvalo]

The settings max_conns and max_idle_conns are not removed from DSN string when hydra connects to Postgres.

If DATABASE_URL is set like this:

DATABASE_URL="postgres://pghost:5432/hydra?sslmode=disable&max_conns=20&max_idle_conns=4"

Hydra can't connect to the Postgres.
Postges logs:

2019-03-27 13:22:22.615 GMT [41732] FATAL:  unrecognized configuration parameter "max_idle_conns"
2019-03-27 13:22:37.629 GMT [41734] FATAL:  unrecognized configuration parameter "max_conns"

[aeneasr]

Please use the issue templates. Crucial information is missing, like software version, command you executed, and so on. This issue will auto-close otherwise.

[vesvalo]

Command to run:

export DATABASE_URL="postgres://pghost:5432/hydra?sslmode=disable&max_conns=20&max_idle_conns=4"
hydra serve all --dangerous-force-http

Environment, software version: kubernetes, docker image hydra:v1.0.0-rc.6_oryOS.10-alpine

The issue was addressed in the #464, but that fix is not present in the repository now.