Remove unused MCSection::empty

CurFragList->Head should be non-null, so empty() is not useful.

Author: MaskRay

llvm/include/llvm/MC/MCSection.h

@@ -181,7 +181,6 @@ class MCSection {
   FragList *curFragList() const { return CurFragList; }
   iterator begin() const { return iterator(CurFragList->Head); }
   iterator end() const { return {}; }
-  bool empty() const { return !CurFragList->Head; }
 
   void dump() const;