Remove unexpected target_os "bitrig"

    error: unexpected `cfg` condition value: `bitrig`
      --> argp/src/term_size/unix.rs:18:5
       |
    18 |     target_os = "bitrig",
       |     ^^^^^^^^^^^^^^^^^^^^
       |
       = note: expected values for `target_os` are: `aix`, `android`, `cuda`, `dragonfly`, `emscripten`, `espidf`, `freebsd`, `fuchsia`, `haiku`, `hermit`, `horizon`, `hurd`, `illumos`, `ios`, `l4re`, `linux`, `macos`, `netbsd`, `none`, `nto`, `nuttx`, `openbsd`, `psp`, `redox`, `rtems`, `solaris`, `solid_asp3`, `teeos`, `trusty`, `tvos`, `uefi`, `unknown`, `visionos`, `vita`, and `vxworks` and 5 more

argp/src/term_size/unix.rs

@@ -15,7 +15,6 @@ static TIOCGWINSZ: c_ulong = 0x5413;
 #[cfg(any(
     target_os = "macos",
     target_os = "ios",
-    target_os = "bitrig",
     target_os = "dragonfly",
     target_os = "freebsd",
     target_os = "netbsd",