-Werror,-Wunused-macros

"VC_EXTRALEAN can only be used in MFC projects."
(<https://support.microsoft.com/en-us/kb/166474> "How to use VC_EXTRALEAN and
WIN32_LEAN_AND_MEAN to enhance the build process in Visual C++")

So presumably indeed not needed here (as reported by clang-cl).

Change-Id: Id98c6e9e862e716cf5e238623c6ac4ca0603fd63

clew/source/clew.c

@@ -14,7 +14,6 @@
 #ifndef CLCC_GENERATE_DOCUMENTATION
     #ifdef _WIN32
         #define WIN32_LEAN_AND_MEAN
-        #define VC_EXTRALEAN
         #include <windows.h>
 
         typedef HMODULE             CLCC_DYNLIB_HANDLE;