Cleanup

Thanks to glfwGetKeyScancode we can now pass only a scancode to the
platform layer for glfwGetKeyName.

src/null_window.c

@@ -261,7 +261,7 @@ const char* _glfwPlatformGetClipboardString(_GLFWwindow* window)
     return NULL;
 }
 
-const char* _glfwPlatformGetKeyName(int key, int scancode)
+const char* _glfwPlatformGetScancodeName(int scancode)
 {
     return "";
 }