skip likeliness annotation in BitVectorReader ctor

Summary: The smallest codegen is just to emit `test ; je ; mov` where the control may conditionally skip over just the `mov`. Likeliness annotations make the codegen larger and more complicated for little gain.

Reviewed By: Orvid

Differential Revision: D48155222

fbshipit-source-id: a03ae71f5d81883a307a25cb38983286f3155f69

folly/experimental/BitVectorCoding.h

@@ -252,8 +252,7 @@ class BitVectorReader : detail::ForwardPointers<Encoder::forwardQuantum>,
         detail::SkipPointers<Encoder::skipQuantum>(list.skipPointers),
         bits_(list.bits),
         size_(list.size),
-        upperBound_(
-            (kUnchecked || UNLIKELY(list.size == 0)) ? 0 : list.upperBound) {
+        upperBound_(kUnchecked || list.size == 0 ? 0 : list.upperBound) {
     reset();
   }