Internals: Color densely in V3Graph::weaklyConnected, and return the count

No algorithm depends on this, so can be changed, later improvement will.
No functional change.

src/V3Reorder.cpp

@@ -293,7 +293,6 @@ class ReorderVisitor final : public VNVisitor {
         for (AstNode* currp = nodep; currp; currp = currp->nextp()) {
             ReorderLogicVertex* const vtxp = currp->user3u().to<ReorderLogicVertex*>();
             const uint32_t color = vtxp->color();
-            UASSERT_OBJ(color, currp, "No node color assigned");
             if (lastOfColor[color]) new ReorderStrictEdge{m_graphp, lastOfColor[color], vtxp};
             lastOfColor[color] = vtxp;
         }