(Due 1/1/2026) - Remove File/Builder feature flag from Log4jLogManager

[jtduffy]

Description

For CrAC support, the configuration of the agent's root logger was moved to the Log4j Configuration Builder from a file based configuration. A FF flag was introduced to revert back to file based config in cause issues came up using the Builder. This FF needs to be removed after several months.

• Remove all file based config code from Log4jLogManager
• Remove FF check
• Remove /META-INF/logging/log4j2.xml from the project

[workato-integration]

https://new-relic.atlassian.net/browse/NR-374145