Update hex-simd expected output

Previously, the `hex-simd` benchmark retrieved the bytes to hexify from
its own WebAssembly binary. This self-referential use was prone to
breakage any time the `benchmark.wasm` changed, like from building with
a new version of Rust. The `stdout.expected` file would immediately be
out of date. To fix this, this change randomly dumps 1MB of data into
`default.input` (as other benchmarks do) and uses this as the input to
hexify.

benchmarks/hex-simd/rust-benchmark/src/main.rs

@@ -8,7 +8,7 @@ use std::arch::x86::*;
 use std::arch::x86_64::*;
 
 fn main() {
-    let input = std::fs::read("./benchmark.wasm").unwrap();
+    let input = std::fs::read("./default.input").unwrap();
     let mut dst = vec![0; 2 * input.len()];
     bench::start();
     let s = hex_encode(&input, &mut dst).unwrap();