stdlib: Remove stdlib README.md

This README.md is outdated and incompleted. User's wishing to learn
about the gem5 stdlib should reference the gem5 website:
https://www.gem5.org/documentation/gem5-stdlib/overview

Issue-on: https://gem5.atlassian.net/browse/GEM5-1019
Change-Id: Ib66bd748d517708833ac591515601f206ce4728a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/55323
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56244
1 file changed