ci(bashlib): drop the dead bc-based NONCE (perf + reliability) (#40691)

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/bashlib.sh

@@ -20,10 +20,6 @@ set -e
 GITHUB_WORKSPACE=${GITHUB_WORKSPACE:-.}
 ASSETS_MANIFEST="$GITHUB_WORKSPACE/superset/static/assets/manifest.json"
 
-# Rounded job start time, used to create a unique Cypress build id for
-# parallelization so we can manually rerun a job after 20 minutes
-NONCE=$(echo "$(date "+%Y%m%d%H%M") - ($(date +%M)%20)" | bc)
-
 # Echo only when not in parallel mode
 say() {
   if [[ $(echo "$INPUT_PARALLEL" | tr '[:lower:]' '[:upper:]') != 'TRUE' ]]; then