HDFS-16719. Remove unused import in hadoop-hdfs module

[ZanderXu]

Description of PR

During reading code of hadoop-hdfs module, I found that there are some unused import in some classes, such as unused import TrustedChannelResolver in WhitelistBasedTrustedChannelResolver.java

//WhitelistBasedTrustedChannelResolver.java useless import
import org.apache.hadoop.hdfs.protocol.datatransfer.TrustedChannelResolver 

[ayushtkn]

If the build passes.
Changes LGTM

[slfan1989]

LGTM +1

[ayushtkn]

And I take that back Post reading the comment from @steveloughran here:
#4390 (comment)

So, lets not bother the imports, Anyway I don't think unused imports have any performance impact during runtime, so let them stay

[ZanderXu]

Thanks @slfan1989 @ayushtkn for your review. I will read https://github.com/steveloughran/formality/blob/master/styleguide/styleguide.md carefully and close this PR.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 56s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
-1 ❌	test4tests	0m 0s		The patch doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	38m 49s		trunk passed
+1 💚	compile	1m 44s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	compile	1m 39s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	1m 24s		trunk passed
+1 💚	mvnsite	1m 43s		trunk passed
+1 💚	javadoc	1m 24s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 51s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 43s		trunk passed
+1 💚	shadedclient	23m 27s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	1m 22s		the patch passed
+1 💚	compile	1m 28s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javac	1m 28s		the patch passed
+1 💚	compile	1m 19s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	1m 19s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	1m 2s		hadoop-hdfs-project/hadoop-hdfs: The patch generated 0 new + 75 unchanged - 9 fixed = 75 total (was 84)
+1 💚	mvnsite	1m 27s		the patch passed
+1 💚	javadoc	0m 58s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	1m 28s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	3m 17s		the patch passed
+1 💚	shadedclient	22m 27s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	411m 1s		hadoop-hdfs in the patch passed.
+1 💚	asflicense	1m 15s		The patch does not generate ASF License warnings.
		522m 11s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4710/1/artifact/out/Dockerfile
GITHUB PR	#4710
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 21d4a827d4d0 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 523c9f8
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1 /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-4710/1/testReport/
Max. process+thread count	2833 (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-4710/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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