Improve code style and remove obsolete lines

examples/rpl-border-router/common/border-router-common.c

examples/rpl-border-router/common/httpd-simple.c

examples/rpl-border-router/common/httpd-simple.h

examples/rpl-border-router/common/webserver.c

examples/rpl-border-router/embedded/border-router-embedded.c

examples/rpl-border-router/native/border-router-cmds.c

examples/rpl-border-router/native/border-router-mac.c

examples/rpl-border-router/native/border-router-native.c

examples/rpl-border-router/native/project-conf.h

examples/rpl-border-router/native/slip-config.c

examples/rpl-border-router/native/slip-dev.c

examples/rpl-border-router/native/tun-bridge.c