ci: Remove CircleCI configuration (#3065)

CI is now performed via Github Actions. Some notable Github Action
workflows that replace the CircleCI jobs are:

- test: replaces CCI build, test-api, test-sdk
- test-sql: replaces CCI test-sql
- make-gen-delta: replaces CCI make-gen-delta

See:
    https://github.com/hashicorp/boundary/actions/workflows/test.yml
    https://github.com/hashicorp/boundary/actions/workflows/test-sql.yml
    https://github.com/hashicorp/boundary/actions/workflows/make-gen-delta.yml
    https://docs.github.com/en/actions
    https://cli.github.com/manual/gh_run

scripts/build.sh

@@ -16,10 +16,6 @@ DIR="$( cd -P "$( dirname "$SOURCE" )/.." && pwd )"
 # Change into that directory
 cd "$DIR"
 
-if [ "${CI_BUILD}x" != "x" ]; then
-    [[ -f /home/circleci/.bashrc ]] && source /home/circleci/.bashrc
-fi
-
 # Set build tags
 BUILD_TAGS="${BUILD_TAGS:-"boundary"}"
 echo "==> Build tags: ${BUILD_TAGS}"
@@ -62,10 +58,6 @@ if [ "${SKIP_PLUGIN_BUILD}x" == "x" ]; then
     $DIR/scripts/plugins.sh
 fi
 
-if [ "${CI_BUILD}x" != "x" ]; then
-    exit
-fi
-
 BASE_PRODUCT_VERSION=${BASE_PRODUCT_VERSION:=$(cat version/VERSION)}
 
 # Declare binary paths!