Revert "Update source for Rust 1.66.1"

Revert submission 2421642-rust-update-prebuilts-1.66.1

Reason for revert: Missing riscv support and out of date base64 crate causing brekages

Reverted changes: /q/submissionid:2421642-rust-update-prebuilts-1.66.1

Change-Id: I4264f336e3651fbe4a9130921cbceb8fae01100a
diff --git a/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs b/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs
index a79fa7f..8267cf0 100644
--- a/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs
+++ b/fuzzing/orphans/hashbrown/hashbrown_hashmap_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use hashbrown::HashMap;
 use libfuzzer_sys::arbitrary::Arbitrary;
diff --git a/fuzzing/orphans/hashbrown/hashbrown_hashset_fuzzer.rs b/fuzzing/orphans/hashbrown/hashbrown_hashset_fuzzer.rs
index 4bc4a65..3eb7baf 100644
--- a/fuzzing/orphans/hashbrown/hashbrown_hashset_fuzzer.rs
+++ b/fuzzing/orphans/hashbrown/hashbrown_hashset_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use hashbrown::HashSet;
 use libfuzzer_sys::arbitrary::Arbitrary;
diff --git a/fuzzing/orphans/hashlink/hashlink_linkedhashmap_fuzzer.rs b/fuzzing/orphans/hashlink/hashlink_linkedhashmap_fuzzer.rs
index ef35fd1..65ea227 100644
--- a/fuzzing/orphans/hashlink/hashlink_linkedhashmap_fuzzer.rs
+++ b/fuzzing/orphans/hashlink/hashlink_linkedhashmap_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use hashlink::LinkedHashMap;
 use libfuzzer_sys::arbitrary::Arbitrary;
diff --git a/fuzzing/orphans/hashlink/hashlink_linkedhashset_fuzzer.rs b/fuzzing/orphans/hashlink/hashlink_linkedhashset_fuzzer.rs
index 83260c8..0135a9d 100644
--- a/fuzzing/orphans/hashlink/hashlink_linkedhashset_fuzzer.rs
+++ b/fuzzing/orphans/hashlink/hashlink_linkedhashset_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use hashlink::LinkedHashSet;
 use libfuzzer_sys::arbitrary::Arbitrary;
diff --git a/fuzzing/orphans/hashlink/hashlink_lrucache_fuzzer.rs b/fuzzing/orphans/hashlink/hashlink_lrucache_fuzzer.rs
index 19910f3..a5cc957 100644
--- a/fuzzing/orphans/hashlink/hashlink_lrucache_fuzzer.rs
+++ b/fuzzing/orphans/hashlink/hashlink_lrucache_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use hashlink::LruCache;
 use libfuzzer_sys::arbitrary::Arbitrary;
diff --git a/fuzzing/orphans/smallvec/smallvec_fuzzer.rs b/fuzzing/orphans/smallvec/smallvec_fuzzer.rs
index ce62e3a..be96564 100644
--- a/fuzzing/orphans/smallvec/smallvec_fuzzer.rs
+++ b/fuzzing/orphans/smallvec/smallvec_fuzzer.rs
@@ -14,6 +14,7 @@
 
 #![allow(missing_docs)]
 #![no_main]
+#![feature(bench_black_box)]
 
 use libfuzzer_sys::arbitrary::Arbitrary;
 use libfuzzer_sys::fuzz_target;