Remove obsolete code. (#1121)

This NetBSD constant is now upstream.

Author: sunfishcode

src/backend/libc/c.rs

@@ -86,11 +86,6 @@ pub(crate) const XCASE: tcflag_t = linux_raw_sys::general::XCASE as _;
 #[cfg(target_os = "aix")]
 pub(crate) const MSG_DONTWAIT: c_int = libc::MSG_NONBLOCK;
 
-// TODO: Remove once <https://github.com/rust-lang/libc/pull/3377> is merged and released.
-#[cfg(target_os = "netbsd")]
-#[cfg(feature = "net")]
-pub(crate) const SO_NOSIGPIPE: c_int = 0x0800;
-
 // It is defined as 0 in libc under 64-bit platforms, but is automatically set
 // by kernel. <https://github.com/torvalds/linux/blob/v6.7/fs/open.c#L1458-L1459>
 #[cfg(linux_kernel)]