Update source for Rust 1.66.1

This CL removes a feature flag for a stabilized feature.

Bug: 263153841
Test: m rust
Change-Id: I2b5b0c2207b1eae29bb75a94b9df2664fd82b25e
diff --git a/pvmfw/avb/src/lib.rs b/pvmfw/avb/src/lib.rs
index 8fea162..d83737f 100644
--- a/pvmfw/avb/src/lib.rs
+++ b/pvmfw/avb/src/lib.rs
@@ -15,8 +15,6 @@
 //! A library implementing the payload verification for pvmfw with libavb
 
 #![cfg_attr(not(test), no_std)]
-// For usize.checked_add_signed(isize), available in Rust 1.66.0
-#![feature(mixed_integer_ops)]
 
 mod descriptor;
 mod error;