test(ffi): remove the toBuffer no-finalizer workaround

[EffortlessSteven]

Stacked on oven-sh#31753 for review. Do not merge into the base branch; this gets rebased onto upstream/main and submitted upstream after oven-sh#31753 lands.

What this does

oven-sh#35246 enabled the compiled FFI fixture cross-platform and, in the same hunk, scoped primitives' Buffer and added a Bun.gc(true) after it. That collection segfaults, because toBuffer without a finalizer adopted the caller's pointer as owned, so the test passes getNoopDeallocatorCallback() to avoid it. oven-sh#31753 fixes the path, so the callback now only hides coverage of it.

Fix: drop the callback so the compiled fixture exercises the real default: wrap static native storage, drop the Buffer, force GC, then read the pointer again. getNoopDeallocatorCallback has no other users, so it goes too.

Verification

Red without oven-sh#31753, green with it: on a Bun lacking the fix the fixture takes down the whole test runner with panic(main thread): Segmentation fault at address 0x8420. That is the crash oven-sh#35405 reports, and since oven-sh#35246 the fixture runs on Windows too, so this callback is what currently keeps CI from seeing it.

Check	Result
bun bd test ffi/ffi.test.js -t primitives	2 passed, both runner variants
getDeallocatorCallback, getDeallocatorBuffer, getDeallocatorCalledCount	kept, still exercised
no remaining getNoopDeallocatorCallback references	rg clean across src/ and test/
prettier	clean

Review map

• test/js/bun/ffi/ffi.test.js: primitives calls toBuffer(cptr, 0, 4) and toArrayBuffer(cptr, 0, 4) with no finalizer; symbol descriptor and destructuring entry removed.
• test/js/bun/ffi/ffi-test.c: getNoopDeallocatorCallback and its noop_deallocator removed.

[EffortlessSteven]

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Walkthrough

Changes

FFI deallocator callback removal

Layer / File(s)	Summary
Remove noop deallocator symbol test/js/bun/ffi/ffi-test.c, test/js/bun/ffi/ffi.test.js	The native noop deallocator export and its JavaScript FFI symbol declarations and destructuring are removed.
Use borrowed pointer storage test/js/bun/ffi/ffi.test.js	The primitives test converts the borrowed static pointer without a deallocator finalizer and documents that GC must not free it.

Suggested reviewers: jarred-sumner

🚥 Pre-merge checks | ✅ 4

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title is concise and accurately summarizes the main change: removing the no-finalizer FFI workaround.
Description check	✅ Passed	The description covers the PR purpose and verification clearly; it only uses non-template section headings.

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