examples: remove dead increments

examples: remove dead increments

Fixes following error reported by clang-9 analyzer:

 examples/server.c:244:2: warning: Value stored to 'argc' is never read
        argc -= optind;
        ^       ~~~~~~

 examples/server.c:245:2: warning: Value stored to 'argv' is never read
        argv += optind;
        ^       ~~~~~~

Signed-off-by: Petr Štetiar <ynezz@true.cz>