Revert "Add network interface flag constants for all platforms"

src/unix/bsd/apple/mod.rs

src/unix/bsd/freebsdlike/dragonfly/mod.rs

src/unix/bsd/freebsdlike/freebsd/mod.rs

src/unix/bsd/freebsdlike/mod.rs

src/unix/bsd/netbsdlike/netbsd/mod.rs

src/unix/bsd/netbsdlike/openbsdlike/mod.rs

src/unix/haiku/mod.rs

src/unix/newlib/mod.rs

src/unix/solaris/mod.rs

src/unix/uclibc/mod.rs