improve: remove duplicate forceGarbageCollection setValue in run method

[shoothzj]

Motivation

remove duplicate forceGarbageCollection setValue, it is redundant and error-prone. It's already seted in

bookkeeper/bookkeeper-server/src/main/java/org/apache/bookkeeper/bookie/GarbageCollectorThread.java

Lines 473 to 478 in 945cfa1

	} finally {
	if (force && forceGarbageCollection.compareAndSet(true, false)) {
	LOG.info("{} Set forceGarbageCollection to false after force GC to make it forceGC-able again.",
	Thread.currentThread().getName());
	}
	}

[StevenLuMT]

LGTM

[shoothzj]

@dlg99 @eolivelli @hangc0276 @merlimat @nicoloboschi @zhaijack PTAL