Revert r194865 and r194874.

This change is incorrect. If you delete virtual destructor of both a base class
and a subclass, then the following code:
  Base *foo = new Child();
  delete foo;
will not cause the destructor for members of Child class. As a result, I observe
plently of memory leaks. Notable examples I investigated are:
ObjectBuffer and ObjectBufferStream, AttributeImpl and StringSAttributeImpl.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194997 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/Hexagon/HexagonSubtarget.h

@@ -42,7 +42,6 @@ public:
 
 public:
   HexagonSubtarget(StringRef TT, StringRef CPU, StringRef FS);
-  virtual ~HexagonSubtarget();
 
   /// getInstrItins - Return the instruction itineraies based on subtarget
   /// selection.