Do not define ENUM_BITFIELDS_NOT_SUPPORTED for MSVC (#230)

In order to move to OSS React Native, Windows needs to define
ENUM_BITFIELDS_NOT_SUPPORTED. This causes warnings treated as errors on
the microsoft fork due to macro redefinition. Remove the code that
automatically adds this definiion.

This allows the removal of the YGStyle patch added to RNW. At item was
created to remove this entire chunk once we're off the fork.

Author: NickGerleman

ReactCommon/yoga/yoga/YGStyle.h

@@ -17,12 +17,6 @@
 #include "Yoga.h"
 
 
-// Until we sync past this: https://github.com/facebook/react-native/commit/a7e4ce0f0d83b6162d77db7d680e838666f6d938#diff-140c478f1096be49a1b121931a7680ee
-// We have to turn off the bitfield usage for MSVC builds
-#ifdef _MSC_VER
-#define ENUM_BITFIELDS_NOT_SUPPORTED
-#endif
-
 #if !defined(ENUM_BITFIELDS_NOT_SUPPORTED)
 #define BITFIELD_ENUM_SIZED(num) : num
 #else