CI: don't remove dependencies of coq-mathcomp-zify

coq-mathcomp-algebra and coq-mathcomp-fingroup re-installed when
installing coq-mathcomp-zify, so don't remove them in the first place

.gitlab-ci.yml

@@ -21,7 +21,7 @@ stages:
   stage: build
   script:
     - opam update -y
-    - opam remove -y coq-mathcomp-algebra coq-mathcomp-character coq-mathcomp-field coq-mathcomp-fingroup coq-mathcomp-solvable  # Check coq-mathcomp-ssreflect is enough
+    - opam remove -y coq-mathcomp-character coq-mathcomp-field coq-mathcomp-solvable  # Check coq-mathcomp-ssreflect is enough
     - opam pin add -n -y -k path coq-prosa .
     - opam install -y -v -j ${NJOBS} coq-prosa