remove unused layout graph pool

[star-e]

Re: #

Changelog

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

---

Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

[github-actions]

Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1009831 bytes	1009831 bytes	✅ 0 bytes
2D All (legacy pipeline)	2675390 bytes	2675390 bytes	✅ 0 bytes
2D All (new pipeline)	2767126 bytes	2765610 bytes	👍 -1516 bytes
(2D + 3D) All	10024124 bytes	10022608 bytes	👍 -1516 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16843186 bytes	16841670 bytes	👍 -1516 bytes

Interface Check Report

This pull request does not change any public interfaces !

[star-e]

@cocos-robot run-test-cases-custom

[github-actions]

@star-e, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v3.8.8
• Task Result: FAIL
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/9fc43f15-c3a0-4a9e-b579-55199068c1b9/-1
• GitHub Action: https://github.com/cocos/cocos-engine/actions/runs/19421378425

Task Details

Platform	build	boot	runned	crashScene	FailScene
web-mobile	PASS	PASS	FAIL
ios	PASS	PASS	FAIL
mac	PASS	PASS	FAIL		particle-compare

[github-actions]

@star-e, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v3.8.8
• Task Result: FAIL
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/093ccf10-ffe1-469c-ad1b-8d86114167a7/-1
• GitHub Action: https://github.com/cocos/cocos-engine/actions/runs/19421378425

Task Details

Platform	build	boot	runned	crashScene	FailScene
windows	PASS	PASS	FAIL		particle-compare