Revert "Add a _LIBCPP_ELAST configuration for MINGW."

This reverts commit af97e6d31636794e59bad0be8e3744ae2bc58621.
diff --git a/include/__config b/include/__config
index d8dc240..7cb0881 100644
--- a/include/__config
+++ b/include/__config
@@ -644,8 +644,6 @@
 #define _LIBCPP_ELAST __ELASTERROR
 #elif defined(__APPLE__)
 // Not _LIBCPP_ELAST needed on Apple
-#elif defined(__MINGW__)
-#define _LIBCPP_ELAST EWOULDBLOCK
 #else
 // Warn here so that the person doing the libcxx port has an easier time:
 #warning This platform's ELAST hasn't been ported yet