[clangd] Remove the dead offset fields in Symbol.

clangd/index/Index.h

struct SymbolLocation {
   struct Position {
     uint32_t Line = 0; // 0-based
     // Using UTF-16 code units.
     uint32_t Column = 0; // 0-based
   };
 
   // The URI of the source file where a symbol occurs.
   llvm::StringRef FileURI;
-  // The 0-based offsets of the symbol from the beginning of the source file,
-  // using half-open range, [StartOffset, EndOffset).
-  // DO NOT use these fields, as they will be removed immediately.
-  // FIXME(hokein): remove these fields in favor of Position.
-  unsigned StartOffset = 0;
-  unsigned EndOffset = 0;
 
   /// The symbol range, using half-open range [Start, End).
   Position Start;
   Position End;
 
   operator bool() const { return !FileURI.empty(); }
 };
 llvm::raw_ostream &operator<<(llvm::raw_ostream &, const SymbolLocation &);