Delete .gitlab-ci.yml

.gitlab-ci.yml

-stages:
-    - build
-  
-build_and_test:
-    image: rboman/waves
-    stage: build
-    script:
-        - source ./envs/linux-macos.sh
-        - cd lib && ./get_gmsh.sh && cd ..
-        - mkdir build
-        - cd build
-        - cmake ..
-        - make -j 4