mon/QuorumService.h: remove unused QuorumService::flags

CID 1019626 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
  uninit_member: Non-static class member "flags" is not initialized
  in this constructor nor in any functions that it calls.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>