Remove superfluous 'virtual' specifiers in ART.

Remove 'virtual' specifier on methods already bearing the 'override'
specifier.

Test: mmma art
Change-Id: I114930969a5ca048d88de9ecd18e2c6403593e31
diff --git a/libdexfile/dex/dex_file_loader.cc b/libdexfile/dex/dex_file_loader.cc
index d9e483d..400c32b 100644
--- a/libdexfile/dex/dex_file_loader.cc
+++ b/libdexfile/dex/dex_file_loader.cc
@@ -36,7 +36,7 @@
 class VectorContainer : public DexFileContainer {
  public:
   explicit VectorContainer(std::vector<uint8_t>&& vector) : vector_(std::move(vector)) { }
-  virtual ~VectorContainer() override { }
+  ~VectorContainer() override { }
 
   int GetPermissions() override {
     return 0;