Remove dead Meta ecosystem build steps from the Alpine Dockerfile

Delete the commented-out Folly/Fizz/Wangle/mvfst/fbthrift/CacheLib RUN
blocks instead of carrying them as dead code; keep a short explanatory
comment in the Dockerfile and move the fuller rationale to
INCLUDED_LIBRARIES.md, scoped explicitly to alpine3.24 since debian13
and rockylinux9 are glibc-based and build the full Meta stack.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WGpSs9pKTbvPkmFvBaWhBp

INCLUDED_LIBRARIES.md

@@ -46,3 +46,5 @@
 | libxml2 | `2.15.3` |
 
 The image includes position-independent static builds of these libraries. Protobuf and libxml2 enable zlib support, and LibDwarf enables compressed debug section support using zlib and Zstd. ZeroMQ enables CURVE security using static libsodium. CZMQ enables UUID support using static util-linux libuuid while disabling undeclared optional integrations. librdkafka includes SSL, zlib, Zstd, and bundled LZ4 support while disabling undeclared optional integrations. spdlog uses external fmt, glog uses gflags, and all Meta libraries share the same release tag.
+
+**Alpine-only exception:** the `alpine3.24` image does not build Folly, Fizz, Wangle, mvfst, fbthrift, or CacheLib. These aren't on Meta's supported-OS list, and Folly's portability layer reaches for glibc-only macros/symbols with no musl branch (e.g. `off64_t`/`lseek64`/`pread64` in `folly/portability/Unistd.h`, `__ELF_NATIVE_CLASS` in `folly/debugging/symbolizer/Elf.cpp`), so patching each one as it surfaces risks introducing subtle bugs in code this project doesn't own. `debian13` and `rockylinux9` are glibc-based and build the full list above, Meta libraries included.