[CI] remove old e-acsl CI config

src/plugins/e-acsl/.gitlab-ci.yml

-stages:
- - git-update
- - build
- - tests
-
-variables:
-    CURRENT: $CI_COMMIT_REF_NAME
-    DEFAULT: "master"
-    OCAML: "4_05"
-    FRAMA_CI_OPT: "--override e-acsl:$CI_COMMIT_REF_NAME,$CI_COMMIT_SHA"
-
-
-#avoid a nix error https://github.com/NixOS/nix/issues/2087
-git-update:
-  stage: git-update
-  script:
-   - nix/frama-ci.sh instantiate --eval -A e-acsl.src.outPath
-  tags:
-   - nix
-
-E-ACSL:
-  stage: build
-  script:
-   - nix/frama-ci.sh build -A e-acsl.installed
-  tags:
-   - nix
-
-CheckHeaders:
-  stage: build
-  script:
-   - nix/frama-ci.sh build -A genassigns.checkHeaders
-  tags:
-   - nix
-
-Tests:
-  stage: tests
-  script:
-   - nix/frama-ci.sh build -A e-acsl.tests
-  tags:
-   - nix
-
-Tests-dev:
-  stage: tests
-  script:
-   - nix/frama-ci.sh build -A e-acsl.tests-dev
-  tags:
-   - nix
-
-Cfp:
-  stage: tests
-  script:
-   - nix/frama-ci.sh build -A context-from-precondition.tests
-  tags:
-   - nix
-
-Security:
-  stage: tests
-  script:
-   - nix/frama-ci.sh build -A security.tests
-  tags:
-   - nix