maint(ci): remove Slither (#12411)

Slither hasn't been useful for a long time. Refer to issue #12410
for more context.

.github/workflows/slither.yml

-name: 'Slither Analysis'
-
-on:
-  workflow_dispatch:
-  pull_request:
-  push:
-    branches:
-      - develop
-
-jobs:
-  slither-analyze:
-    runs-on: ubuntu-latest
-    container:
-      image: us-docker.pkg.dev/oplabs-tools-artifacts/images/ci-builder:v0.49.0
-    steps:
-      - uses: actions/checkout@v4
-
-      - name: Run Slither
-        uses: crytic/slither-action@v0.4.0
-        id: slither
-        with:
-          target: packages/contracts-bedrock
-          slither-config: packages/contracts-bedrock/slither.config.json
-          fail-on: config
-          sarif: results.sarif
-          slither-args: --triage-database packages/contracts-bedrock/slither.db.json
-
-      - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@v3
-        if: always()
-        with:
-          sarif_file: ${{ steps.slither.outputs.sarif }}