Remove unnecessary #ifndef NDEBUG guard around assert. NFC.

Found by Hal Finkel in the review of AttributeSets.  http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20150504/275058.html

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@236662 91177308-0d34-0410-b5e6-96231b3b80d8

lib/IR/Attributes.cpp

@@ -819,12 +819,10 @@ AttributeSet AttributeSet::removeAttributes(LLVMContext &C, unsigned Index,
   if (!pImpl) return AttributeSet();
   if (!Attrs.pImpl) return *this;
 
-#ifndef NDEBUG
   // FIXME it is not obvious how this should work for alignment.
   // For now, say we can't pass in alignment, which no current use does.
   assert(!Attrs.hasAttribute(Index, Attribute::Alignment) &&
          "Attempt to change alignment!");
-#endif
 
   // Add the attribute slots before the one we're trying to add.
   SmallVector<AttributeSet, 4> AttrSet;