samples: bpf: Drop doubled variable declaration in xdpsock

Seems that by accident there is a doubled declaration of global variable
opt_xdp_bind_flags in xdpsock_user.c. The second one is uninitialized so
compiler was simply ignoring it.

To keep things clean, drop the doubled variable.

Fixes: c543f546

 ("samples/bpf: add unaligned chunks mode support to xdpsock")
Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Björn Töpel <bjorn.topel@intel.com>
Link: https://lore.kernel.org/bpf/20200205045834.56795-3-maciej.fijalkowski@intel.com