Lex: Remove explicitly deleted copy constructor, NFC

`std::unique_ptr<MemoryBuffer>` already deletes these, so there's no
reason for the boiler-plate in HeaderMap.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@261442 91177308-0d34-0410-b5e6-96231b3b80d8

include/clang/Lex/HeaderMap.h

@@ -30,9 +30,6 @@ namespace clang {
 /// symlinks to files.  Its advantages are that it is dense and more efficient
 /// to create and process than a directory of symlinks.
 class HeaderMap {
-  HeaderMap(const HeaderMap &) = delete;
-  void operator=(const HeaderMap &) = delete;
-
   std::unique_ptr<const llvm::MemoryBuffer> FileBuffer;
   bool NeedsBSwap;