[lld-macho][NFC] Remove redundant member from class Defined

`class Symbol` defines a data member `InputFile *file;`
`class Defined` inherits from `Symbol` and also defines a data member `InputFile *file;` for no apparent purpose.

Differential Revision: https://reviews.llvm.org/D99783

lld/MachO/Symbols.h

@@ -117,7 +117,6 @@ public:
 
   static bool classof(const Symbol *s) { return s->kind() == DefinedKind; }
 
-  InputFile *file;
   InputSection *isec;
   uint64_t value;
   uint64_t size;