The fix for JDK-8359493 added the ability to associate DiagnosticFlag's to specific warnings defined in compiler.properties. In cases where the flag is an inherent property of the warning itself, compiler.properties is a more appropriate place to declare the flag, instead having to add it at all the points in the codebase where that particular warning is used.

In particular, the Log API methods mandatoryWarning() and mandatoryNote() can be removed, as they serve only to add the MANDATORY flag to warnings and notes for which "mandatoryness" is inherent. Doing so will help decomplexify the code a bit.