build(relibc): remove check_against_libc_crate from default features; fix cond import

The libc crate's pthread type layouts do not match Redox's relibc
layouts (e.g. pthread_cond_t 8 vs 12 bytes). Redox is its own libc,
so comparing against a foreign Linux libc crate is not meaningful.
Disable the feature by default and keep relibc types internally
consistent via assert_equal_size! checks against our own Rlct* types.

Cargo.toml

@@ -130,7 +130,7 @@ redox_protocols.workspace = true
 
 [features]
 # to enable trace level, take out this `no_trace`
-default = ["check_against_libc_crate", "ld_so_cache", "no_trace"]
+default = ["ld_so_cache", "no_trace"]
 check_against_libc_crate = ["__libc_only_for_layout_checks"]
 ld_so_cache = []
 math_libm = []

src/header/pthread/cond.rs

@@ -2,8 +2,6 @@
 
 use core::sync::atomic::AtomicU32;
 
-use crate::header::time::CLOCK_REALTIME;
-
 use super::*;
 
 // PTHREAD_COND_INITIALIZER is defined manually in bits_pthread/cbindgen.toml