Remove VS2017_WIN64 generator as it won't compile.

Author: mrijkeboer

build.rs

@@ -8,7 +8,6 @@ fn link_nng() {
     struct Generator(&'static str);
     const UNIX_MAKEFILES: Generator = Generator("Unix Makefiles");
     const NINJA: Generator = Generator("Ninja");
-    const VS2017_WIN64: Generator = Generator("Visual Studio 15 2017 Win64");
     const VS2017: Generator = Generator("Visual Studio 15 2017");
 
     // Compile time settings
@@ -17,15 +16,15 @@ fn link_nng() {
     } else if cfg!(feature = "cmake-ninja") {
         NINJA
     } else if cfg!(feature = "cmake-vs2017-win64") {
-        VS2017_WIN64
+        VS2017
     } else if cfg!(feature = "cmake-vs2017") {
         VS2017
     } else {
         // Default generators
         if cfg!(target_family = "unix") {
             UNIX_MAKEFILES
         } else {
-            VS2017_WIN64
+            VS2017
         }
     };