Remove the unused dockcross wrappers linux-arm64-lts and android-arm

Linux aarch64 builds natively on ubuntu-24.04-arm with GCC 14, so the
linux-arm64-lts cross-compile wrapper has no caller; 32-bit Android was
never built in CI and is not published. README, REUSE.toml, CLAUDE.md
and the stdc++fs comment in CMakeLists.txt no longer name them.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AytmJF9faEiQEVt6eetQS2

Author: claude