HDFS-16529. Remove unnecessary setObserverRead in TestConsistentReadsObserver

[wzhallright]

Remove unnecessary setObserverRead in TestConsistentReadsObserver
JIRA: https://issues.apache.org/jira/browse/HDFS-16529

Description of PR

How was this patch tested?

For code changes:

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 39s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		codespell was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ trunk Compile Tests _
+1 💚	mvninstall	33m 34s		trunk passed
+1 💚	compile	1m 28s		trunk passed with JDK Ubuntu-11.0.14+9-Ubuntu-0ubuntu2.20.04
+1 💚	compile	1m 21s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	0m 59s		trunk passed
+1 💚	mvnsite	1m 27s		trunk passed
+1 💚	javadoc	1m 6s		trunk passed with JDK Ubuntu-11.0.14+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	1m 35s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 17s		trunk passed
+1 💚	shadedclient	22m 41s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 14s		the patch passed
+1 💚	compile	1m 21s		the patch passed with JDK Ubuntu-11.0.14+9-Ubuntu-0ubuntu2.20.04
+1 💚	javac	1m 21s		the patch passed
+1 💚	compile	1m 14s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	1m 14s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 51s		the patch passed
+1 💚	mvnsite	1m 17s		the patch passed
+1 💚	javadoc	0m 53s		the patch passed with JDK Ubuntu-11.0.14+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	1m 27s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 16s		the patch passed
+1 💚	shadedclient	22m 14s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	228m 15s		hadoop-hdfs in the patch passed.
+1 💚	asflicense	0m 46s		The patch does not generate ASF License warnings.
		328m 47s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4131/1/artifact/out/Dockerfile
GITHUB PR	#4131
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux dfd9ca8efa53 4.15.0-169-generic #177-Ubuntu SMP Thu Feb 3 10:50:38 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / aaf0d13
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.14+9-Ubuntu-0ubuntu2.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4131/1/testReport/
Max. process+thread count	3640 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs U: hadoop-hdfs-project/hadoop-hdfs
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4131/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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[aajisaka]

Thank you @wzhallright and @tomscut