TEZ-4650: Remove useless logic from AM plugin management: processSchedulerDescriptors

[abstractdog]

See: jira description

Additional local testing:

1. removed the method
2. rebuilt tez 0.10.5
3. ran hive on tez unit test locally:

mvn install -Dtest.output.overwrite=true -Pitests -nsu -pl itests/qtest -Dtest=TestMiniTezCliDriver -Dqfile=acid_vectorization_original_tez.q

Also tez has unit test coverage in this area: in case it's green, this patch is safe.

[abstractdog]

apparently, there is a failing case:

[ERROR]   TestDAGAppMaster.testParseAllPluginsOnlyCustomSpecified:275->verifyDescAndMap:413 expected:<2> but was:<1>

I'm going to investigate this: it seems like this unit test asserts that the yarn plugin descriptor is hacked to the entities even when enableYarn:false, so the application expects it to be present in non-local mode, even when containersEnabled=false...which still seems quite hacky, need to understand what use case this unit test covers

EDIT: in the only 1 known custom plugin use-case, which is Hive LLAP, Hive sets the descriptor to enableYarn:true:
https://github.com/apache/hive/blob/c338904b80d4dc6df08981738b69fa136bf6c624/ql/src/java/org/apache/hadoop/hive/ql/exec/tez/TezSessionState.java#L341
because this calls enableContainers=true case:

tez/tez-api/src/main/java/org/apache/tez/serviceplugins/api/ServicePluginsDescriptor.java

Line 138 in 0a5c714

return new ServicePluginsDescriptor(true, enableUber, null, null, null);

so, this unit test doesn't cover a known use-case
I'm about to remove it or change the asserted values with an explanation in a code comment

[tez-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 🆗	detsecrets	0m 0s		detect-secrets 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.
			_ master Compile Tests _
+1 💚	mvninstall	13m 49s		master passed
+1 💚	compile	0m 47s		master passed
+1 💚	checkstyle	1m 19s		master passed
+1 💚	javadoc	0m 37s		master passed
+0 🆗	spotbugs	2m 35s		tez-dag in master has 785 extant spotbugs warnings.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 31s		the patch passed
+1 💚	codespell	0m 26s		No new issues.
+1 💚	compile	0m 30s		the patch passed
+1 💚	javac	0m 30s		the patch passed
+1 💚	blanks	0m 1s		The patch has no blanks issues.
+1 💚	checkstyle	0m 16s		the patch passed
+1 💚	javadoc	0m 14s		the patch passed
+1 💚	spotbugs	1m 45s		the patch passed
			_ Other Tests _
+1 💚	unit	5m 11s		tez-dag in the patch passed.
+1 💚	asflicense	0m 14s		The patch does not generate ASF License warnings.
		30m 9s

Subsystem	Report/Notes
Docker	ClientAPI=1.51 ServerAPI=1.51 base: https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-433/4/artifact/out/Dockerfile
GITHUB PR	#433
Optional Tests	dupname asflicense javac javadoc unit spotbugs checkstyle codespell detsecrets compile
uname	Linux eda0a00b806e 5.15.0-156-generic #166-Ubuntu SMP Sat Aug 9 00:02:46 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	/home/jenkins/jenkins-home/workspace/tez-multibranch_PR-433/src/.yetus/personality.sh
git revision	master / d5bfce2
Default Java	Ubuntu-21.0.8+9-Ubuntu-0ubuntu124.04.1
Test Results	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-433/4/testReport/
Max. process+thread count	221 (vs. ulimit of 5500)
modules	C: tez-dag U: tez-dag
Console output	https://ci-hadoop.apache.org/job/tez-multibranch/job/PR-433/4/console
versions	git=2.43.0 maven=3.8.7 spotbugs=4.9.3 codespell=2.0.0
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[ayushtkn]

LGTM