Remove Tracer#logClearingTrace()

[schlosna]

Before this PR

LOG4J2-3560 is triggering significant allocations on calls to Logger#isDebugEnabled() such as from Tracer#logClearingTrace()

tracing-java/tracing/src/main/java/com/palantir/tracing/Tracer.java

Lines 911 to 926 in e7da94d

	static void clearCurrentTrace() {
	logClearingTrace();
	currentTrace.set(null);
	MDC.remove(Tracers.TRACE_ID_KEY);
	MDC.remove(Tracers.TRACE_SAMPLED_KEY);
	MDC.remove(Tracers.REQUEST_ID_KEY);
	}
	private static void logClearingTrace() {
	if (log.isDebugEnabled()) {
	log.debug("Clearing current trace", SafeArg.of("trace", currentTrace.get()));
	if (log.isTraceEnabled()) {
	log.trace("Stacktrace at time of clearing trace", new SafeRuntimeException("not a real exception"));
	}
	}
	}

Long term upstream fix for log4j is proposed as apache/logging-log4j2#974 ; however, we may want to consider removing Tracer#logClearingTrace() in the interim as it impacts services that heavily utilize tracing, such as timelock & atlasdb's AwaitingLeadershipProxy

After this PR

==COMMIT_MSG==
Remove Tracer#logClearingTrace()
==COMMIT_MSG==

Possible downsides?

We lose the debug & trace logging @tpetracca added in #678 though I don't think this is used often if ever.

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Remove Tracer#logClearingTrace()

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[schlosna]

Going to close this out for now, will reopen if needed

[schlosna]

#1413