Remove ILoggerFactory.MinimumLevel

[Eilon]

This property has two things going against it:

1. Everyone thinks it does something other than what it does. (This can be mitigated by a rename of some sort.)
2. It's not needed anymore. It was added to avoid sensitive information being logged inadvertently. This was later decided to be a non-issue.

This is teh codez: https://github.com/aspnet/Logging/blob/dev/src/Microsoft.Extensions.Logging.Abstractions/ILoggerFactory.cs#L14-L17

@lodejard @muratg @DamianEdwards

[lodejard]

👍 this should have been removed a while ago!

[muratg]

Agreed!

@JunTaoLuo 🎁