print_tracing_info() does not use Unified Logging for output

Summary

Convert TraceYoungGenTime and TraceOldGenTime to use unified logging and thus remove the flags.

Problem

Most of the GC logging has been converted to use unified logging and can be turned on using the correct tags. For some reason TraceYoungGenTime and TraceOldGenTime is still around and the logging doesn't follow the normal format.

Solution

Remove the two flags and let the same logging be available under the tag-set "gc, heap, exit" on the "debug" level. This tag-set is currently used to display other information about the heap during shutdown, and these times fit fairly well under the same set.

Specification

The change basically consists of changing the printing to use unified logging and changing the checks against the flags similar to:

-    if (TraceYoungGenTime) accumulated_time()->start();
+    if (log_is_enabled(Debug, gc, heap, exit)) accumulated_time()->start();