osdc/Objecter: drop unused field

osdc/Objecter: drop unused field

This as missed by 860d72770cdf092c027d50f4ee03bed76c975599.

** CID 1204296:  Uninitialized scalar field  (UNINIT_CTOR)
/osdc/Objecter.h: 1165 in Objecter::Op::Op(const object_t &, const
object_locator_t &, std::vector<OSDOp, std::allocator<OSDOp>> &, int, Context *,
Context *, unsigned long *)()
/osdc/Objecter.h: 1165 in Objecter::Op::Op(const object_t &, const
object_locator_t &, std::vector<OSDOp, std::allocator<OSDOp>> &, int, Context *,
Context *, unsigned long *)()

Signed-off-by: Sage Weil <sage@inktank.com>