Remove bazel from repo (quantumlib#4297)

Fixes quantumlib#4280

Author: MichaelBroughton

.github/workflows/ci.yml

@@ -191,11 +191,6 @@ jobs:
       - name: Install requirements
         run: |
           pip install -r dev_tools/requirements/deps/protos.txt
-          sudo apt install curl gnupg
-          curl -fsSL https://bazel.build/bazel-release.pub.gpg | gpg --dearmor > bazel.gpg
-          sudo mv bazel.gpg /etc/apt/trusted.gpg.d/
-          echo "deb [arch=amd64] https://storage.googleapis.com/bazel-apt stable jdk1.8" | sudo tee /etc/apt/sources.list.d/bazel.list
-          sudo apt update && sudo apt install bazel
       - name: Build protos
         run: check/build-changed-protos
   coverage:
@@ -335,4 +330,4 @@ jobs:
       - name: Install npm dependencies
         run: check/npm ci
       - name: Test
-        run: check/ts-coverage
+        run: check/ts-coverage

WORKSPACE

@@ -71,30 +71,9 @@ if [[ ! -z "$changed" ]]; then
     done
 fi
 
-# Check if any of the build files have changed.
-build_changed=$(git diff --name-only ${rev} -- \
-    | grep "google/api/.*BUILD$" \
-    | sed -e "s/BUILD//")
-
-if [[ -z "$build_changed" ]]; then
-    echo -e "No BUILD files changed."
-else
-    # Build all the targets for the changed BUILD rule.
-    echo -e "BUILD file changed in directories: '${build_changed[@]}'"
-    for build_prefix in $build_changed
-    do
-        (set -x; bazel build "${build_prefix}...:*")
-    done
-fi
-
-# We potentially will attempt to build a second time, but this is not
-# a problem as bazel returns immediately.
+# We potentially will attempt to build a second time.
 for base in $changed
 do
-    (set -x; bazel build "${base}_proto"; \
-    bazel build "${base}_py_proto"; \
-    bazel build "${base}_cc_proto")
-
     python -m grpc_tools.protoc -I=cirq-google --python_out=cirq-google --mypy_out=cirq-google ${base}.proto
 done
 
@@ -109,4 +88,4 @@ if [[ ! -z "$untracked" ]]; then
         echo -e "\033[31m   ${generated}\033[0m"
     done
     exit 1
-fi
+fi

check/build-changed-protos

@@ -151,10 +151,6 @@ Cirq's protobufs live at [cirq/api/google](https://github.com/quantumlib/Cirq/tr
 If any protos are updated, their dependents can be rebuilt by calling the script [dev_tools/build-protos.sh](https://github.com/quantumlib/Cirq/tree/master/dev_tools).
 This script uses grpcio-tools and protobuf version 3.8.0 to generate the python proto api.
 
-Additionally, for workflows that use bazel (relevant for C/C++ code depending on Cirq), we have made available bazel rulesets for generating both python and C/C++ proto apis.
-These rules live in the BUILD files [here](https://github.com/quantumlib/Cirq/tree/master/cirq/api/google/v1) and [here](https://github.com/quantumlib/Cirq/tree/master/cirq/api/google/v2).
-Downstream projects should load Cirq as an [external dependency](https://docs.bazel.build/versions/master/external.html), allowing rules from those BUILD files to be used directly.
-
 ## Continuous integration and local testing
 
 There are a few options for running continuous integration checks, varying from easy and fast to slow and reliable.