Remove usage of slice_internals feature

This CL replaces the usage of the core::slice::memchr function with
calls to std::iter::position.

Test: m keystore2_unsafe_fuzzer
Test: TH
Bug: 267698452
Change-Id: I33cab09176d0ff02ce092e240e887ece98728915
diff --git a/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs b/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
index 3291190..0dca3a2 100644
--- a/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
+++ b/keystore2/src/fuzzers/keystore2_unsafe_fuzzer.rs
@@ -14,11 +14,9 @@
 
 //! Fuzzes unsafe APIs of libkeystore2 module
 
-#![feature(slice_internals)]
 #![no_main]
 
 use binder::get_declared_instances;
-use core::slice::memchr;
 use keystore2::{legacy_blob::LegacyBlobLoader, utils::ui_opts_2_compat};
 use keystore2_aaid::get_aaid;
 use keystore2_apc_compat::ApcHal;
@@ -38,7 +36,7 @@
 
 /// CString does not contain any internal 0 bytes
 fn get_valid_cstring_data(data: &[u8]) -> &[u8] {
-    match memchr::memchr(0, data) {
+    match data.iter().position(|&b| b == 0) {
         Some(idx) => &data[0..idx],
         None => data,
     }