Update the use of perceval gitee backend.

[heming6666]

As the perceval backend for Gitee has migrated form https://github.com/WillemJiang/grimoirelab-perceval to https://github.com/WillemJiang/grimoirelab-perceval-gitee, we need to update the use of gitee backend.

[WillemJiang]

Once we separate the git-elk part from grimoirelab-elk, we don't need to add the requirement of the grimoirelab-perceval-gitee.