Remove empty core::lazy and std::lazy

PR #98165 with commits 7c360dc117 and c1a2db3372
has moved all of the components of these modules into different places,
namely {std,core}::sync and {std,core}::cell. The empty
modules remained. As they are unstable, we can simply remove them.

library/std/src/lib.rs

@@ -529,9 +529,6 @@ pub mod process;
 pub mod sync;
 pub mod time;
 
-#[unstable(feature = "once_cell", issue = "74465")]
-pub mod lazy;
-
 // Pull in `std_float` crate  into libstd. The contents of
 // `std_float` are in a different repository: rust-lang/portable-simd.
 #[path = "../../portable-simd/crates/std_float/src/lib.rs"]