flake.lock: roll iserv-proxy back to 8cdc446 (drop aarch64-android stubs)
Reverts the two stub commits 0b8d6f6 / 3d649af in stable-haskell/iserv-proxy (`flake.lock` was bumped to them in haskell.nix commits 3303ea332 / 11c3abf88). Those commits added local definitions of bionic-absent symbols (`__cxa_guard_acquire`, `__cxa_guard_release`, `__fadvise64`, `__getpriority`, `__ldtoa`, `__sflush`, `__vfprintf`, `async_safe_fatal_no_abort`, `async_safe_format_buffer`) to `cbits/symbols.aarch64-android.c` to satisfy ld.lld during a link where they were undefined. In the current build configuration (NDK 27, current cabal flags, ghc 9.14.1) those symbols already resolve cleanly without the stubs — and the stubs were displacing the real bionic / libc++ implementations at runtime, causing the qemu segfault on aarch64-android iserv-proxy-interpreter that we'd been tracking as a separate "qemu builder" issue. Verified `tests.js-template-haskell.build` on `ghc9141.aarch64-android-prebuilt` passes with the override `--override-input iserv-proxy github:stable-haskell/iserv-proxy/8cdc446f` on linux-0 with `--builders ''`: iserv-proxy-interpreter links and runs under qemu-aarch64 with no segfault.