cpplint: Cleanup errors

Cleanup errors from upstream cpplint in preparation
for moving art's cpplint fork to upstream tip-of-tree cpplint.

Test: cd art && mm
Bug: 68951293
Change-Id: I15faed4594cbcb8399850f8bdee39d42c0c5b956
diff --git a/compiler/utils/atomic_dex_ref_map.h b/compiler/utils/atomic_dex_ref_map.h
index fad056c..205543f 100644
--- a/compiler/utils/atomic_dex_ref_map.h
+++ b/compiler/utils/atomic_dex_ref_map.h
@@ -29,7 +29,7 @@
 template <typename DexFileReferenceType, typename Value>
 class AtomicDexRefMap {
  public:
-  explicit AtomicDexRefMap() {}
+  AtomicDexRefMap() {}
   ~AtomicDexRefMap() {}
 
   // Atomically swap the element in if the existing value matches expected.