Remove faulty assertion in llvm-pdbutil

If a class's first data member is an instance of an empty class, then an
assertion in the PrettyClassLayoutGraphicalDumper would fail. The
storage is reserved, but it's not marked as in use.

As far as I understand, it's the assertion that's faulty, so I removed it
and updated the nearby comment.

Found by running llvm-pdbutil against its own PDB, and this assertion would
fail on HashAdjusters, which is a HashTable whose first data member is a
TraitsT, which is a PdbHashTraits<T>, which is an empty struct. (The struct
has a specialization for uint32_t, but that specialization doesn't apply
here because the T is actually ulittle32_t.)

Differential Revision: https://reviews.llvm.org/D45645

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330135 91177308-0d34-0410-b5e6-96231b3b80d8

tools/llvm-pdbutil/PrettyClassLayoutGraphicalDumper.cpp

@@ -50,12 +50,9 @@ bool PrettyClassLayoutGraphicalDumper::start(const UDTLayoutBase &Layout) {
     uint32_t RelativeOffset = Item->getOffsetInParent();
     CurrentAbsoluteOffset = ClassOffsetZero + RelativeOffset;
 
-    // Since there is storage there, it should be set!  However, this might
-    // be an empty base, in which case it could extend outside the bounds of
-    // the parent class.
+    // This might be an empty base, in which case it could extend outside the
+    // bounds of the parent class.
     if (RelativeOffset < UseMap.size() && (Item->getSize() > 0)) {
-      assert(UseMap.test(RelativeOffset));
-
       // If there is any remaining padding in this class, and the offset of the
       // new item is after the padding, then we must have just jumped over some
       // padding.  Print a padding row and then look for where the next block