[ci/gitlab] Remove after_switch message (not useful anymore).
[ci/gitlab] Remove after_switch message (not useful anymore).

This was put in place for @coqbot to detect runner failures, but now
the strategy is different.

silene/coq,gares/coq,JasonGross/coq,Matafou/coq,ejgallego/coq,coq/coq,JasonGross/coq,gares/coq,SkySkimmer/coq,gares/coq,gares/coq,coq/coq,silene/coq,ejgallego/coq,Zimmi48/coq,ejgallego/coq,JasonGross/coq,SkySkimmer/coq,Matafou/coq,Zimmi48/coq,SkySkimmer/coq,ppedrot/coq,JasonGross/coq,coq/coq,ppedrot/coq,coq/coq,SkySkimmer/coq,ppedrot/coq,Zimmi48/coq,ppedrot/coq,Zimmi48/coq,ppedrot/coq,Matafou/coq,silene/coq,gares/coq,ejgallego/coq