libbinder_ndk_unit_test: set threadpool max to 0

This still allows one binder thread in the thread pool, and one main
thread that drives the test.

Test: libbinder_ndk_unit_test
Bug: 319210610
Change-Id: Iaaba8bf641b3fb9a31aaa298c75327d853727be6

Author: devinmoore-goog

libs/binder/ndk/tests/libbinder_ndk_unit_test.cpp

@@ -984,7 +984,7 @@ int main(int argc, char* argv[]) {
         return generatedFlaggedService(test_flags, kBinderNdkUnitTestServiceFlagged);
     }
 
-    ABinderProcess_setThreadPoolMaxThreadCount(1);  // to receive death notifications/callbacks
+    ABinderProcess_setThreadPoolMaxThreadCount(0);
     ABinderProcess_startThreadPool();
 
     return RUN_ALL_TESTS();