Remove -Wuninitialized for GCC in Expected.h (#1143)

Summary:
- Old versions of GCC (specifically, GCC 4.7) warn about uninitialized memory
  in `Expected.h`
- Newer versions of GCC do not complain, so remove the pragma push/pop which
  was disabling the warning.
Pull Request resolved: https://github.com/facebook/folly/pull/1143

Reviewed By: ericniebler

Differential Revision: D15586279

Pulled By: yfeldblum

fbshipit-source-id: 7b01934c7601ecf035f1e05f2ed3e5f799cf25b9

folly/Expected.h

@@ -52,17 +52,6 @@
 
 #define FOLLY_REQUIRES(...) template <FOLLY_REQUIRES_IMPL(__VA_ARGS__)>
 
-/**
- * gcc-4.7 warns about use of uninitialized memory around the use of storage_
- * even though this is explicitly initialized at each point.
- */
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wuninitialized"
-#pragma GCC diagnostic ignored "-Wpragmas"
-#pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
-#endif // __GNUC__
-
 namespace folly {
 
 /**
@@ -1406,10 +1395,6 @@ bool operator>(const Value& other, const Expected<Value, Error>&) = delete;
 
 } // namespace folly
 
-#if defined(__GNUC__) && !defined(__clang__)
-#pragma GCC diagnostic pop
-#endif
-
 #undef FOLLY_REQUIRES
 #undef FOLLY_REQUIRES_TRAILING