Remove some unused buildbot files (#30476)

etc/ci/buildbot_steps.yml

@@ -1,45 +0,0 @@
-env:
-  RUST_BACKTRACE: '1'
-  RUSTFLAGS: -Dwarnings
-  CARGO_INCREMENTAL: "0"
-  GST_DEBUG: '3'
-  SCCACHE_IDLE_TIMEOUT: "1200"
-  SCCACHE_MAX_FRAME_LENGTH": "100000000"  # 100 MB
-linux-rel-nogate:
- env:
-   CC: clang-4.0
-   CXX: clang++-4.0
- commands:
-  - ./mach clean-nightlies --keep 3 --force
-  - ./mach clean-cargo-cache --keep 3 --force
-  - ./etc/ci/clean_build_artifacts.sh
-  - ./mach build --release -p servo
-  - python ./etc/ci/chaos_monkey_test.py
-  - env RUSTFLAGS= bash ./etc/ci/mutation_test.sh
-  - ./etc/ci/clean_build_artifacts.sh
-
-# Moved to Taskcluster
-linux-dev: []
-mac-dev-unit: []
-windows-msvc-dev: []
-android-mac: []
-android: []
-android-x86: []
-mac-rel-wpt1: []
-mac-rel-wpt2: []
-mac-rel-wpt3: []
-mac-rel-wpt4: []
-mac-rel-css1: []
-mac-rel-css2: []
-android-nightly: []
-windows-msvc-nightly: []
-mac-nightly: []
-linux-nightly: []
-linux-rel-wpt: []
-linux-rel-css: []
-
-# No longer maintained
-arm32: []
-arm64: []
-mac-rel-intermittent: []
-linux-rel-intermittent: []

etc/ci/clean_build_artifacts.sh

@@ -1,12 +0,0 @@
-#!/usr/bin/env bash
-
-# This Source Code Form is subject to the terms of the Mozilla Public
-# License, v. 2.0. If a copy of the MPL was not distributed with this
-# file, You can obtain one at https://mozilla.org/MPL/2.0/.
-
-set -o errexit
-set -o nounset
-set -o pipefail
-
-rm -rf target/
-rm -rf python/_virtualenv*/