[Fish] Ajoute fisher et fish-ssh-agent + remove useless functions

.config/fish/conf.d/fish-ssh-agent.fish

@@ -0,0 +1,7 @@
+if test -z "$SSH_ENV"
+    set -xg SSH_ENV $HOME/.ssh/environment
+end
+
+if not __ssh_agent_is_started
+    __ssh_agent_start
+end