Drop stale J9 MALLOC_CHECK_ skip (PROF-15360 fixed as PROF-15364)

The skip's only justification was PROF-15360, closed as invalid in
favor of PROF-15364 (isRawPointer() false-positive, fixed by this PR).
No separate J9 heap-corruption issue is on record, so J9 now gets the
same MALLOC_CHECK_/MALLOC_PERTURB_ coverage as glibc/HotSpot.

Author: jbachorik

build-logic/conventions/src/main/kotlin/com/datadoghq/profiler/ProfilerTestPlugin.kt

@@ -208,14 +208,11 @@ class ProfilerTestPlugin : Plugin<Project> {
             // Turn silent glibc heap corruption (e.g. a use-after-free write into a
             // freed chunk) into an immediate, attributable SIGABRT instead of a crash
             // much later in an unrelated allocation. Only meaningful against glibc's
-            // own malloc: skip on musl (no MALLOC_CHECK_ support), skip whenever a
-            // sanitizer/allocator already replaces malloc via LD_PRELOAD, and skip on
-            // J9 (its own allocator usage trips a pre-existing, unrelated heap
-            // corruption that needs separate investigation — see PROF-15360).
+            // own malloc: skip on musl (no MALLOC_CHECK_ support), and skip whenever a
+            // sanitizer/allocator already replaces malloc via LD_PRELOAD.
             if (PlatformUtils.currentPlatform == Platform.LINUX &&
                 !PlatformUtils.isMusl() &&
-                !testEnv.containsKey("LD_PRELOAD") &&
-                !PlatformUtils.isTestJvmJ9()
+                !testEnv.containsKey("LD_PRELOAD")
             ) {
                 put("MALLOC_CHECK_", "3")
                 put("MALLOC_PERTURB_", (1..255).random().toString())