Revert "add git to build multi version doc"

This reverts commit b2f82df5.

.gitlab-ci.yml

@@ -23,7 +23,6 @@ build_docs:
       
   stage: build_docs
   script:
-    - apt-get update && apt-get install -y git
     - pip install -r docs/requirements.txt
     - sphinx-multiversion docs/source/ build/html