Remove @backtrace_string in ExceptionLoggingSubscriber::onClientError()

Backtrace removed from the error and checked by generating a 401 error. Please review it.

Know it's a task but should this have test coverage?

Abhijith S → made their first commit to this issue’s fork.

Looking at how #3167390: ExceptionLoggingSubscriber should not log backtrace string on access denied exceptions → was done this was done the same and does contain simple test coverage that the key is gone.

Committed/pushed to 11.x and cherry-picked to 10.2.x, thanks!

Automatically closed - issue fixed for 2 weeks with no activity.