Revert "[compiler-rt][nfc] DenseMap needs placement new (#133329)"

This reverts commit 4485e25.
Buildbot failures, e.g. https://lab.llvm.org/buildbot/#/builders/66/builds/11827

Author: mtrofin

compiler-rt/lib/sanitizer_common/sanitizer_dense_map.h

@@ -19,9 +19,6 @@
 #include "sanitizer_common.h"
 #include "sanitizer_dense_map_info.h"
 #include "sanitizer_internal_defs.h"
-// Placement-new is needed for bucket allocation. This avoids needing to include
-// it everywhere we use DenseMap.
-#include "sanitizer_placement_new.h"
 #include "sanitizer_type_traits.h"
 
 namespace __sanitizer {