Drop workaround for clang-3.6 in Range ctor

Summary: [Folly] Drop workaround for clang-3.6 in `Range` ctor.

Reviewed By: gkmhub, Orvid

Differential Revision: D16945307

fbshipit-source-id: d70d7560375d0c020b19fbac227767605459a834

folly/Range.h

@@ -188,9 +188,7 @@ class Range {
   // Works only for random-access iterators
   constexpr Range(Iter start, size_t size) : b_(start), e_(start + size) {}
 
-#if !__clang__ || __CLANG_PREREQ(3, 7) // Clang 3.6 crashes on this line
   /* implicit */ Range(std::nullptr_t) = delete;
-#endif
 
   constexpr /* implicit */ Range(Iter str)
       : b_(str), e_(str + constexpr_strlen(str)) {