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Reason for revert: Missing riscv support and out of date base64 crate causing brekages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: I6c0d6c3539e766012570e4542f529706fe49928c