Revert "[NFC][LSAN] Limit the number of concurrent threads is the test"

This reverts commit 2a73b7b.

This appears to be causing the following failures on GreenDragon:
  LeakSanitizer-AddressSanitizer-x86_64 :: TestCases/many_threads_detach.cpp
  LeakSanitizer-Standalone-x86_64 :: TestCases/many_threads_detach.cpp

First failure:
    http://green.lab.llvm.org/green/job/clang-stage1-RA/20754/

Still failing in latest build:
    http://green.lab.llvm.org/green/job/clang-stage1-RA/20928/

compiler-rt/test/lsan/TestCases/many_threads_detach.cpp

@@ -3,8 +3,6 @@
 // Use `-pthread` so that its driver will DTRT (ie., ignore it).
 // RUN: %clangxx_lsan %s -o %t -pthread && %run %t
 
-#include <assert.h>
-#include <dirent.h>
 #include <pthread.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -14,33 +12,15 @@
 // reused.
 static const size_t kTestThreads = 10000;
 
-// Limit the number of simultaneous threads to avoid reaching the limit.
-static const size_t kTestThreadsBatch = 100;
-
 void *null_func(void *args) {
   return NULL;
 }
 
-int count_threads() {
-  DIR *d = opendir("/proc/self/task");
-  assert(d);
-  int count = 0;
-  while (readdir(d))
-    ++count;
-  closedir(d);
-  assert(count);
-  return count;
-}
-
 int main(void) {
-  for (size_t i = 0; i < kTestThreads; i += kTestThreadsBatch) {
-    for (size_t j = 0; j < kTestThreadsBatch; ++j) {
-      pthread_t thread;
-      assert(pthread_create(&thread, NULL, null_func, NULL) == 0);
+  for (size_t i = 0; i < kTestThreads; i++) {
+    pthread_t thread;
+    if (pthread_create(&thread, NULL, null_func, NULL) == 0)
       pthread_detach(thread);
-    }
-    while (count_threads() > 10)
-      sched_yield();
   }
   return 0;
 }