Rust 1.78 Upgrade For Linux 6.10, Dropping In-Tree "alloc" Fork To Save ~10k Lines

There's another Rust upgrade coming for the Linux 6.10 kernel to bump the Rust version baseline required for building the Rust in-tree kernel components. This raising of the baseline will continue until a suitable minimum version is achieved where official Rust compiler "just works" well with the Rust'ed kernel bits. The Rust upgrade in Linux 6.10 also does away with its in-tree "alloc" fork for big code savings and simplifying maintenance...