Revert "Only lookup `config.log_level` for stdlib `::Logger`. Closes #11665."

This reverts commit e2b2539468e2f0109ca309ed9ade53edbcc156a2.

Conflicts:
	railties/CHANGELOG.md

We expect loggers to quack like stdlib logger. If log4r needs different
level= assignment, using a Logger-quacking wrapper is the way to do it.

Fixes #14114.