VcsCommand: Get rid of setCookie()

Remove cookie arg from finished() signal, as it's not used
currently. Thus, remove setCookie() method.

Change-Id: Iedd328aece776eebd2d161a36ec28370b8bc4bfc
Reviewed-by: Orgad Shaneh <orgads@gmail.com>

src/plugins/vcsbase/vcsbaseclient.h

@@ -115,8 +115,7 @@ public:
                         const QStringList &arguments,
                         VcsBaseEditorWidget *editor = nullptr,
                         bool useOutputToWindow = false,
-                        unsigned additionalFlags = 0,
-                        const QVariant &cookie = {}) const;
+                        unsigned additionalFlags = 0) const;
 
 protected:
     void resetCachedVcsInfo(const Utils::FilePath &workingDir);