Remove comment lines from the git commit message (as git commit -F does not do that)

Reviewed-by:  dt <qtc-committer@nokia.com>
 enter the commit message for your changes. Lines starting

src/plugins/git/gitsubmiteditor.h

@@ -54,6 +54,8 @@ public:
     void setCommitData(const CommitData &);
     GitSubmitEditorPanelData panelData() const;
 
+    virtual QString fileContents() const;
+
 signals:
     void diff(const QStringList &unstagedFiles, const QStringList &stagedFiles);