match lowering: Remove the `make_target_blocks` hack This hack was introduced 4 years ago in [`a1d0266` (#60730)](https://github.com/rust-lang/rust/pull/60730/commits/a1d0266878793bc8b2bf50958eb529005ed19da0) to improve LLVM optimization time, specifically noticed in the `encoding` benchmark. Measurements today indicate it is no longer needed. r? `@matthewjasper`