[libunwind] Remove an unused variable

src/Unwind-seh.cpp

 
 /// Common implementation of SEH-style handler functions used by Itanium-
 /// style frames.  Depending on how and why it was called, it may do one of:
 ///  a) Delegate to the given Itanium-style personality function; or
 ///  b) Initiate a collided unwind to halt unwinding.
 _LIBUNWIND_EXPORT EXCEPTION_DISPOSITION
 _GCC_specific_handler(PEXCEPTION_RECORD ms_exc, PVOID frame, PCONTEXT ms_ctx,
                       DISPATCHER_CONTEXT *disp, __personality_routine pers) {
-  unw_context_t uc;
   unw_cursor_t cursor;
   _Unwind_Exception *exc;
   _Unwind_Action action;
   struct _Unwind_Context *ctx = nullptr;
   _Unwind_Reason_Code urc;
   uintptr_t retval, target;
   bool ours = false;