Remove doc of cargo signals-based-traps feature (#12643)

This was removed awhile back, so remove the misleading documentation.

Closes #12634

Author: alexcrichton

crates/wasmtime/src/lib.rs

@@ -365,12 +365,6 @@
 //!   with the same overhead as the `call-hook` feature where entries/exits into
 //!   WebAssembly will have more overhead than before.
 //!
-//! * `signals-based-traps` - Enabled by default, this enables support for using
-//!   host signal handlers to implement WebAssembly traps. For example virtual
-//!   memory is used to catch out-of-bounds accesses in WebAssembly that result
-//!   in segfaults. This is implicitly enabled by the `std` feature and is the
-//!   best way to get high-performance WebAssembly.
-//!
 //! More crate features can be found in the [manifest] of Wasmtime itself for
 //! seeing what can be enabled and disabled.
 //!